Crystal Palace Park in south London still hosts a weekly circuit series on a much reduced course no longer the full motor racing circuit. Crystal Palace played host to the World Cyclo-Cross Championships in 1973 and many rounds of the GLC London Champs before it fell out of use.
A few seasons ago Addiscombe CC enquired about its availability only to be repulsed. When the GLC was abolished the park in south London was taken over by Bromley Local Authority who really just didn’t seem that keen on cycle racing in the park. It was a bit of a battle to keep the circuits going let alone cyclo-cross.
World Cyclo Cross Championships – 1973
John Mullineaux National Champs 1970
John Mullineaux National Amateur Champs 1968
Cycle Cross (1968)
Motor race from 1964 showing the full circuit https://www.youtube.com/watch?v=bWp-0TuY4Sk
Tony Bartlett also posted a great bit of film from over 30 years ago: https://www.facebook.com/tony.bartlett.39/videos/1057479400942324/