Thanks to all so far:
BPF - not disagreeing, but I don't have an installed radio and I think in this day and age all are called for. I have an Airspace Aware which meets my needs for GPS and moving map.
@patowalker:
The CAA specifically says that the handheld radios are only permitted within the UK. As a handheld radio isn't part of the aircraft, I'm not certain that the acceptance of our permit aircraft necessarily means a radio being used from within it but that isn't part of it, is also accepted.