My first task is to persuade Helena Kennedy to sit down. "Sit down?" she queries as though I've proposed a mildly perverse way of conducting an interview. "Yes. Then we can begin." She does as she's told but with a little moue to indicate that she's not altogether happy with the arrangement. "And what sort of things are you going to ask me?" she says as I get out my notes. "I haven't really got anything to say about humanism. That's what you call it, isn't it? That's the name of the magazine?" I'm feeling a little like a pompous teacher faced by a precocious pupil. I may have persuaded Baroness Kennedy to sit down but I'm already wondering how I'm going to come up with enough interesting questions to keep her seated for the next 60 minutes. Helena is not someone who ever sits for long. She is always on the move, always between important committee meetings and debates in the Lords and media interviews and court appearances. I must have met her about twenty times in my life but every one of those encounters has been more like an interchange between two relay runners than a social transaction: a quick kiss on both cheeks, a one line reference to common acquaintances ("How's darling Cathie? Seen anything of Mary?") and then she's off on her next lap.

"Take me back to your childhood in Glasgow," I say, somewhat aware that I'm about to address a series of leading questions to a formidable QC. "You came from a family of Labour activists and also a very Catholic family?" "Yes, that's right. In my family Catholicism and socialism were at the heart of our existence. They simply ran in parallel. My father was a trade union man who always had his rosary in his pocket. Like I do now. And we were not just occasional Catholics. We were every Sunday morning Catholics. We prayed. My uncle was a priest. We knew nuns. Catholicism was the stuff of our existence".

Had she ever been involved in any sectarian conflict when she was growing up? "Oh yes. We were always kept in on the 12 July. My mum would haul us all in because she was frightened that we'd be assaulted. In fact the Orange parade used to gather at the bottom of our road and my mother even kept us away from the window. She was convinced that we were identifiable because our eyes were too close together or too far apart."

I'm slightly surprised by her non-judgmental tone. For someone who has repeatedly got herself into trouble for attacking the government's attitude towards civil liberties - her most recent intervention was to suggest that David Blunkett had learned his jurisprudence from Robert Mugabe - she seemed rather complacent about the manner in which sectarianism infringed her liberty to walk the streets of Glasgow. Hadn't she been furious at the activities of the Orange Lodge?

"Not really. We didn't know many Protestants. My mother's closest friend when she grew up in the Gorbals was a Jewish woman called Celia Katz and my mum remained very close to Celia always. We were really much closer to Jewishness than we were to Protestantism. We heard about incidents between Catholics and Protestant but we didn't experience them directly."

But had she ever had doubts about the validity of her own religion when she saw the hostility it was capable of evoking? Or was her Catholicism simply part of the natural order, just taken for granted?

"Oh no. We did think about it. I remember coming back from church one night with my maiden aunt when I was about 14 or 15 and saying to her, 'Do you ever think that maybe there isn't a God? And her response was immediate. 'Go and wash your mouth out with carbolic and get you to confession immediately.'"

Had she found anyone else to talk to her about her doubts? What about her father? Did he have any doubts? "No, I don't think he ever did. Of course, lots of people he knew were communists but he never had any doubts about the existence of God. Socialism and religion were bound together. We were brought up to believe that material things were not important and that people had to be measured by what they did for other people. That was the only measurement. My mother and father didn't just believe that. They lived it. All the time. People would come to them with their troubles and my mother would go straight to the cupboard and take out some food and put it into a bag and give it to them. They constantly lived their faith and their socialist beliefs."

There was something about the way Helena described that little kitchen scene - the cupboard and the food and the bag - which made it stand out from everything else that she'd told me of her childhood. It was as though it were a scene she constantly replayed. As though it directly addressed her dislike of materialism. "That's absolutely true. Money has never been a factor in my life. Of course, being a barrister has meant that I've been able to live a very different life from of my parents, but I don't like people making decisions based on the possibility of earning more money, rather than on principles. I don't like people's intoxication with wealth. I hate it. I'm always disappointed when I see our governors, our supposed masters, gallivanting about with the rich of the world." "Like spending their holidays with Berlusconi?" I suggest gently. "I prefer to put it in a bland form rather than being specific. But I do not like people who are impressed by wealth. I do not like it."

It's impossible not to be impressed by Helena when she is astride a principle. Anyone who strikes an expedient or pragmatic note when confronted by one of her principles had better watch out. One such encounter prompted an entire book. "It was one of the occasions when I was called to book by a whip for voting against the government on a civil liberties issue. He said to me that my concerns were completely out of touch for the voters. For them it was 'just law'. Not anything serious like health or education or the economy. Just law. I left the meeting with my heart as heavy as stone." It didn't take her long to retaliate. Her book Just Law appeared less than a year later and is a wonderfully angry and finely argued denunciation of the manner in which New Labour's cavalier attitude towards the law has led to a drastic reduction in our traditional freedoms.

This makes me wonder about the areas of Helena's life which are not informed by principles. How, for example, does she reconcile her views on human rights with the teaching of the Catholic Church? Wasn't that something of an intellectual struggle in her adolescence? "Oh yes. I became very doubtful about religion then. And a lot of my rage against organised religion was about what it did to women and how it sold the poor the great beyond as a distraction from the here and now. And I became aware of how religion restricted reproductive choice for women. And I always remember the hypocrisy. How some Catholics could obtain annulments to their marriage from the Church because they had money."

But weren't all those aspects of Catholicism still present? And if they were how was it that she could still describe herself as a believer? Still take communion? Did she accept such other central tenets of the religion as the divinity of Christ and the resurrection and the afterlife and heaven and hell? She dodged my question. "Well, my mother is now 91 and it is rather wonderful to hear her confidence and enthusiasm about shedding the mortal coil and going off to meet my dad. Although she is a rather worried she might not recognise him because her memory is now a bit off."

"But you surely know that she is not going to meet your dad?" "What I know is that it is not going to be like she thinks it is going to be. I do think there is a way in which people live on. I do think that there is somewhere a hand shaping it all." "A higher being?" I suggest. "I don't want to talk about beings. That's too anthropomorphic. But I think there is a shape and order somewhere. Some intellectual force. But I don't want people to set themselves up as moral authorities on such matters. I believe in the secular state. I hate the idea that we are expanding rather than retracting religious schools. I do not want to see a society develop where more and more people are identified by their religious convictions. I think that going down the road of having more and more religious schools is a disaster."

But if she is still a practising Catholic, doesn't she want to make more and more converts? Isn't it a Catholic duty to save souls from the devil and from the falsities of other religions?

"Yes, I do still retain a sense of my Catholicism. It is irrational. It is. And it runs in parallel to my rational world. The indoctrination that I had as a child stays with me. And I like big parts of it. I like the business of participating in a ritual. I like that. I like ritual. I like the fact that there is a requiem mass to celebrate the end of someone's life. I like the fact that there are baptisms and christenings. I like the fact that we celebrate moments in life's journey. That is why people seek out religion. It provides them with those moments, those footprints along the way."

In the years that I've been carrying out these interviews for New Humanist, I've become aware of how often people concentrate on the pleasures of rituals when they are describing any residual value that organised religion might still hold for them. So, in a way, there was nothing too surprising about Helena Kennedy's fondness for 'footprints along the way'. But I sense that these rituals really only make sense for her if they are informed by some sort of religious belief. I tried again. "Look, I know that you keep telling me your Catholicism isn't the same as your parents', that you don't believe literally in all the Catholic dogmas, but I'm still trying to find out what it is that you do accept. Do you want to say that you have some sense of the transcendent which you want to call 'God'."

"No. I don't want any such dramatic high-flown stuff. All I know is that I am constantly involved in an endeavour to be a better person. I'm not interested in what other people think about me. This is me. Only I know in my soul that I am living my life in terms of what I'd call goodness."

"And when you look out at the world you find it easy to make distinctions between those who are truly good people and those who are not?"

"Yes. I can say that someone is a truly good person. It is usually concerned with how they put themselves at the service of others. That is usually what's important. But there's another goodness. Occasionally I come across someone who has an extraordinary inner serenity, a real stillness and peacefulness. That's what I call 'spiritual'. And that stillness is very seldom part of my existence."

I tell her that she makes such stillness sound remarkably like the Catholic state of grace, the freedom from sin. "Really. Is that something to do with stillness? Then you are absolutely right. It's a stillness that allows a sense of connection with something universal. Something greater than ourselves."

I know by now that there is no point asking Helena to define this 'something greater'. So, I try yet another angle. "Why do you want to be good?" I ask. "What drives you along that path? After all it loses you a lot of friends."

"I suspect you can't be true to yourself without upsetting others. But every so often, even though it can be a painful business, you have to be prepared to stand up for what you think is right. You can't be dictated to by the wish to be popular any more than you can be dictated to by the chance to earn more money."

I tell her that she sounds very stern, very driven by conscience, as though being good, being 'in a state of grace' still had something to do with her Catholic childhood, with wanting to please God. She doesn't reject this notion entirely. She almost seems over eager to admit that she was formed by her childhood. "Was your father a good man?" I ask. She immediately becomes animated.

"He was a truly good man. A truly good man. Part of my legacy comes from that and from Catholicism. My father certainly believed. And unlike the other fathers my friends tell me about, he was different in that he really talked to me as a child. I remember being very disappointed when I was not picked for something at school. And he was very serene and philosophical. He said that unless you yourself know pain, unless you yourself experience disappointments, unless you yourself have things go wrong in your life, then you will not be able to understand or empathise with other people's pain and disappointment."

I knew that her father had died quite early in her life, before the birth of any of her three children. To what extent was her life a sort of homage to him, a wish to be as good as he had been?

"Absolutely. Yes. Of course. My father is a lodestone in my life. He gave me the belief that you stand up for what you believe in even if it is going to be painful for you."

Our agreed hour is hardly up, but I notice that Helena's right hand is already resting on the handle of her small wheelie suitcase. Her face and demeanour suggest that she's already preparing for her next engagement. It's probably just as well. I'd have liked to suggest to her that the reason she didn't ever choose to bring her formidable rationalism to bear upon her religion was because that religion was inextricably tangled up with her childhood and particularly with her abiding love and admiration for her father. What she had acquired from him was so precious to her that she was disinclined to question anything about its origins. Her father had been a Catholic and a socialist until the end of his life and if those beliefs were what had made him stick by his principles then they would serve equally well for a daughter confronted by the expediency and cynicism and intellectualism of contemporary metropolitan politics.

She looked up and gave me a broad mischievous smile. "I'm very worried that I'm giving you the impression that I'm Mrs Worthy. I am very concerned about moral issues but I hope in a non-moralistic way. I once said that I'd like to be remembered as 'great fun'. And I am good fun. I'm not always busy lecturing people and shaking my finger at them. I hope to persuade people with wit as well as with experience. But time is short and there is an awful lot to be done. I want an extra hour a day." "You're never going to stop? You're never going to sell out?" "No, I am not going to sell out. But I might drop dead."

I walk down to Reception with her and then watch and she sets off to her next engagement. She's walking in her usual brisk purposeful way, looking straight ahead through clear rational eyes. The only non-heroic element about her is the small suitcase she pulls behind her. I allow myself to imagine that this is where she keeps all those oddly irrational religious elements from her past. But the metaphor doesn't really work. The past doesn't burden Helena Kennedy. It drives her.