Kim: road racing at regional level takes place on open roads (i.e. not closed to other traffic). Courses are usually circuits of around 10 miles, on country roads. The local council and police are informed. Fields of up to 80 can be allowed. Often we run 2 races on the same course at the same time. Each race gets support vehicles, motorbike escorts and static marshals at junctions. No police support for these events.
National races get police cover as well as team cars, publicity vehicles, TV motorbikes etc. Not even the Tour of Britain gets the roads completely shut from start to finish. the British police is very reluctant to do this, what they do is provide a rolling road closure where oncoming traffic is stopped about 15 mins before the race arrives, all the junctions are closed off and normal traffic resumes once the race has passed. Only the Tour de France got the entire route closed off on the day, as that was a condition of the race coming to Britain.
I am not entirely sure why the TCR couldn't run in Britain, as it seems to run like a competitive audax, but I'm not an expert in law.