Extremely difficult, if not entirely impossible.
Experimental is not a term recognised by the EASA/UK CAA system. I think the essential divide these days will be manufactured and kit built. Manufactured will need to satisfy the relevant EASA code (or FAA equivalent if built in the USA). Kit built used to be subject to a special CAA process, which lead to a UK CAA permit to fly. I am not sure whether a system exists under the current system at all. If it does it will be at least as difficult to do as the old system.
I believe there is only one type of kit helicopter that can be built and flown in the UK: the Rotorway (in various versions but including the Exec). I understand that the UK distributor and the USA kit manufacturer took years to get CAA acceptance. I doubt that any indivdiual will have the resources to complete a similar exercise.
You need to ask the CAA, but the answer will be as close to "NO" as makes no difference, I suggest.