Hi Griff
This is off the top of my head so happy to be corrected:
From 8th April 2014, your medical records have to be held by the authority that issues the licence - that does not prevent a medical examiner from another EASA state from carrying out the medical but he will have to send the details to UK if that is where your licence is issued.
If you revalidate/renew a type and the test is carried out by a UK TRE with level 6 ELP, he can sign for your language proficiency on the SRG 2138 examiners report form. You may have to tie that test in with applying for an EASA licence.
Cheers
TeeS