Several events do happen, still all it needs is an act of parliament to get approval then the local councils can apply to have speed limits de restricted for a time limited period.
But motorsport groups have been working on that for years now and it costs a minimum of 10 grand a go - and we are getting nowhere fast.
If your holding a cycle/running race etc then its no problem, but stick on 4 wheels and an engine and its bang your head time