Renew medical, refresher training as required, proficiency check(s), and a bit of paperwork.
Create a CAA customer portal account for e-Licensing and medical records. A fresh initial medical exam will be needed if the medical has lapsed by 5+ years. A UK prof check can be done without a valid medical.
Refresher training isn't mandatory to renew a UK aircraft or instrument rating for which you hold the equivalent third-country rating. FCL.740(b) and FCL.625(e) in Part-FCL annexed to the
UK Aircrew Regulation.
If you're a native English speaker, or as near as, and the examiner holds a level 6 English Language Proficiency endorsement, then you can be assessed as as level 6 during the prof check. More details on On-Track Aviation's
ELP info page.
If you don't use e-Licensing, apply for the conversion on form SRG 1104, and for the ELP assessment on SRG 1199. If you rely on third-country ratings to avoid mandatory refresher training, submit SRG 2142 beforehand.