Didn't they open the park and let them gather in there to get them off the road?
I also remember when things changed at Box Hill. An idiot journalist for one of the London evening papers with a "trendy" column came down and then wrote a BS article titled "The rocker box where bikers roar", that brought hoards of tossers down there, followed by loads of heavy handed police (no doubt the Chief Constable doing a favour for privileged pals who lived nearby) that in due course led to the dedicated bikes only parking space which limited how many could attend.