If you've been away for 4 years, your UK issued licence likely had the word EASA written on the front. Ignore the word EASA, it's just a UK licence.
To get going in the airline world, you'll need to renew an existing type rating. This will mean training as required, then a proficiency check. This can be done in a sim.
If you want to do some GA flying, you'll need to renew your SEP/MEP class rating. Much the same story, training then proficiency check.
Pay attention to the specific airline recruitment requirements. Some want you to have flown the aircraft within the last 6 months, 12 months, 36 months etc. Have a chat with the recruitment teams before spending your hard earned on renewing your own rating - they may well do it for you!
The CAA require you to hold a medical appropriate to the licence held, so Class 1 for airline or Class 2 for GA.
https://www.caa.co.uk/General-aviati...e-type-rating/