englishal
I agree that the CAA could not compel a US trust company to place an aircraft on the G register. However, it would only require a minor amendment to the Air Navigation Order to require anyone who imports a foreign registered aircraft to place it on the G register. As the US trust company is not eligable to own an aircraft on the G register the aircraft it could not permanently import the aircraft.
Such action would be entirely compatible with the Chicago Convention and reflect the approach which I believe is adopted by some other states. For example I understand that Canada and the US both prevent foreign registered aircraft from operating in their airspace if they have been there for more than a set amount (90 days in Canada) within any 12 month period. I think that the problem with the YAKs will have made the CAA give this issue some serious consideration.