I understood the regs changed recently but i may be wrong ..
Road racing is legal in the UK and has been so for many decades. Road racing is generally organised by local clubs and is run under the auspices of British Cycling (and also The League International, to a lesser extent).
Organisers have to do things like liaise with the police, carry out risk assessments, provide marshals for junctions and hazard points and organise lead cars, motorcycle marshals, etc. All participants in BC road races must have a racing licence, and the race itself is insured through BC.
Organising a road race is quite an operation (one of the reasons Sportive avoid classing themselves as races is to avoid this overhead, I believe)
However, races takes place on open roads (the only fully closed road road racing I’m aware of in the UK is on the Isle of Man, excluding town centre crits). Pro events in the UK have used rolling closures in some cases.