The UK allows you to renew the IR without renewing the MEP rating. Other countries argue that you cannot hold an IR without a class rating (MEP, or type etc). So yes, some schools will "force" you to renew the MEP as well.
You can renew anywhere in EASA, the examiner just has to sit through a UK CAA powerpoint to get "certified" for the UK requirements. They then sent the paperwork to Gatwick.
You'll need to renew in the aircraft since your IR is expired. The difference between renewing IR only and IR + MEP is only about 5 minutes of flight time. Basically the only extra thing is an engine out circuit to land. The examiner fee will be higher as well, but really you're only looking at about 150€ extra.
-- Based on personal experience with the renewal process.