DB is correct, the UK CAA appear to have been very pragmatic in their approach. They continue to recognise EASA certificates that were in place on 31st December for a period of up to 2 years or until it's next renewal. This applies to non-UK issued licences, TRE certificates, medicals, simulator certification, etc. They also have a blanket validation for EASA licenced pilots to continue to fly UK registered aircraft.
Has any UK licenced pilot managed to obtain an EASA State validation to fly a commercial aircraft registered to an EASA State?
To pick up on Aucky's earlier Part FCL references, does sub para (c) (2) (i) rule this option out for any training conducted within the EASA states e.g. simulators in France, Italy, Norway or Finland? Has any UK TRE managed to obtain an "EASA" TRE certificate?