I did almost exactly the same thing last year so I can give a fairly definitive answer to your initial question (although it has already been answered by others).
I passed my class 1 in 1987 and spent the next 14 years driving various wagons for various companies but joined the emergency services in 2001 'cos it was (sort of) on offer and I fancied a change. My class 1 expired (as it does) on my 45th birthday and I didn’t bother renewing as I wasn’t using it. Fast forward 17 years and an early retirement scheme was mooted so I applied and got it. To renew my class 1 I only needed to do the medical and send the forms in to DVLA. You’ll need a digital tacho card and a driver CPC also. Do yourself a favour and do the ADR course, it counts towards your DCPC and makes you so much more employable…it’s a useful and practical way to do most of the DCPC.
You’ll need the DVLA forms which I think are here: gov.uk/dvlaforms
And for your digicard, here: gov.uk/government/publicati … river-card
I’m only 53 but coming back into the transport industry has been brilliant, the best thing I’ve done for ages. Good luck and enjoy it!
edit: I had to do the full 35 hours of DCPC before I could turn a wheel, it was pretty tedious and I wish I’d done some of it as ADR