In the early/mid 1990s there were some big free festivals in London parks. Not pseudo-free festivals behind big fences with lots of private security, but proper sprawling mildy-chaotic events with sound systems, dance tents and lots of bands. Two of the biggest were the Deptford Urban Free Festival (in Fordham Park, New Cross) and the Hackney Homeless Festival.
The latter in Clissold Park, Stoke Newington in May 1994 aimed to raise awareness of homelessness, as the name suggests. The energy behind it came out of the squatting scene, but they did involve a locla street homeless hostel, McNaughton House. Up to 30,000 people attended with acts including The Levellers, Co-Creators, Spannerman, Back to the Planet and Fun Da-Mental. One of the stages was organised by Club Dog.
The police piled in after the festival outside the Robinson Crusoe pub, arresting 30 people as clashes erupted. According to one person present: 'A line of police in riot gear approached the pub, pushing people, telling them to go. That's when the glasses started flying. I saw one guy, who asked why they were doing this, get jabbed with a baton. I saw a woman in a wheelchair, who was obviously very distressed, being wheeled around roughly by a police policeman. It was completely unprovoked' (NME, 14 May 1994 - full article below)
Some interesting video footage of the festival at Spectacle video archive.
For more on Hackney, see Radical History of Hackney: http://hackneyhistory.wordpress.com/