some years ago i arrived in London, late in the night. Looking for a camping, endet at a station, a taxi driver explained the way to Brixton.
There i found the crystal palace caravaning club.
There was one way to enter, load off the lugagge and take the small entry, my DR650r needed all space but fitted.
When i was in, a friendly man helped me with the tent, when all was finished he asked for my passport, it was the owner!
I stayed for two nights, very cheap, inclusive a card for bus and tube for this two days.
Bet you can let your rig for the day on the camping ground, if not camping there.
It is a clean place, with a park same named and pretty near the city.