Rarely a day has gone by when I’m working at home that I haven’t walked through Clissold Park, close to where I’ve lived in Hackney for the past 40 years. This afternoon the park was teeming with Orthodox Jewish families, the men in wide fur hats and prayer shawls, the women in severe costume dresses, the children with bikes and scooters, all munching ice creams. The world of the park has always seemed to me a place apart, strangely inviolate, which still resists the blatant commercialisation evident in every other square inch of the modern city. It’s a good example of what the Situationists would have called a TAZ – a temporary autonomous zone – an enclave of self-organised freedom.

Like many other students in 1968 I was swept up in the idealism of the May events, though my fellow trainee teachers and I still spent most of our spare time volunteering on an adventure playground. Not so much street-fighting, more face-painting man. Looking back on those times, it is clear that the Situationists had a more prescient eye on the future than the 57 varieties of Leninism otherwise on offer. There was a brief period when the New Left – with which I was involved – was divided into those who wanted to read Althusser and those who got excited by Saul Alinsky. The latter was a guru of the community-organising politics of those West Coast radicals who thought parks and playgrounds contained the germ of the future utopia.

There is no doubt in my mind that images of children at play which dominated European and American photography after the Second World War – initially through the enormous success of the 1955 Family of Man exhibition organised by Edward Steichen – lit the fuse, so to speak, of the street culture and street theatre of late ’60s radical politics. Many of the photographs portrayed children at play on the streets and bomb-sites in cities around the world, reclaiming them as their natural territory and lost domain. The enragés were simply grown-up children.

The Situationists got much of it right, and their influence is probably as strong today as it was 40 years ago. This is especially so in the marking out of contested political territory, exemplified in the writing of Iain Sinclair and other psychogeographers, whose work enchants and frustrates in equal measure. Nevertheless I detect a waning of interest in the inner city as the last redoubt of authenticity, and a new interest in more open landscapes – especially at the marginal edges – as the coming sphere of meaning. In post-Sinclair times, the writers who have done most to capture the idiosyncrasies and freedoms of the unscripted walk and the spontaneous exploration have been people such as WG Sebald, Roger Deakin, Robert Macfarlane, Jim Perrin and Kathleen Jamie, and all of them at the land’s edges. East Anglia has never been so trendy; Essex is the new Estramaduras.

This is possibly because most city districts – think Hoxton, think Bristol Harbourside, think Liverpool One – have been colonised by dreary urban designers, loft developers, barristers and baristas. And the same is now happening not just to streets but to playgrounds, where planners and designers have little time for any form of unscripted life and leisure. Only last year one of the government’s new school academies opened in Peterborough – designed deliberately without a playground. The head teacher claimed that “I think what the public want is maximum learning.” Yet the world of the park still tantalisingly offers freedoms and pleasures – including the domain of free play – that are beyond the reach of commercialised leisure and the national curriculum. No wonder today’s contrarians are deserting the grey for the green, the pavement for the beach.