If your rating has expired ie. not been revalidated within the last 5 years it can only be renewed by the CAA if its a UK Jar licence, so in practice you do training as required, could include ground school refresher if the tech knowlegde is poor, plus an LST with a TRE, The TRE cannot sign your licence if the rating has expired, all the paperwork goes off to CAA for their consideration
The "IR "is just the rating issued, eg 777 IR, but it is only valid for 12 months (+ a bit to end of month of expiry), so you have to do an LPC every 12 months to use the privileges of the rating.
The issue of your ICAO ATPL and UK ATPL is not of concern as they will issue a UK JAR ATPL if you can demonstrate you meet the requirments, if your 777 rating has expired it may not be included on the UK JAR licence until you do another LPC
SEE STD DOC 43 and FCL 1.25