Really depends on what you want to do with the aircraft,
it is possible to keep an aircraft on the American register
which may be the only viable option for some types due
the difficulty of CAA certification.
This involves some additional housekeeping in the sense
of a trust arrangement and your needing an FAA certificate
to fly it outside UK-airspace.
It has the positive position of allowing use of FAA ratings
and maintenance schedules...however it also prevents
your performing aerial work without a specific exemption.
-- Andrew