The man concerned was an independent socialist who wanted to 'add a bit of revolution to the stalinist obelisk' which is a fair description of Marx's memorial in Highgate cemetery, north London.
Unwisely he went alone, on an on- the- spot whim (which would have been a regular thing to do in the 1960s) and placed a red flag on the grave.
Suddenly a thug leapt out from the bushes with a heavy looking object in hand, yelling, grabbed the flag, broke it, and tried to grab the guys camera too. Thinking him to be a nutter lurking around for a spot of commie bashing, he tried to push him away, at which point the 'thug' radioed for 'help', turning out to be a member of the ground staff!!! a few tourists cowered in the corner while the staff surrounded him and debated what to do, and they were not sympathetic. our socialist had a dilemma; having raised the red flag at marx's memorial, he was not prepeared to comply with thuggish threats and proceeded to make a speech in favor of the world wide struggle against capitalism. having made the point, he departed, and fortunately came to no further harm, walking out while the staff growled insults and followed him to the exit.
he shrugged it off, but it seems that even the most innocuous left wing activity now is dangerous. dont do any activity alone, take a helmet just in case, and never your best camera. as for the ground staff, what a way to behave in a cemetery !