the simple truth is that the change in MOT requirements in may this year is no different to that which occurred when they introduced MOT exemption for vehicles registered before 1st January 1960. You only need an MOT for taxation purposes if the vehicle was built after the qualifying date.
Insurance companies cannot and do not impose rules that are outside of the legal requirement. Roadworthiness and MOT certificates are not related. The responsibility for roadworthiness rests with the rider. I have never yet been asked to prove an MOT certificate was in place as a result of an RTA either before or since the changes.