Rikping:
Well, surprisingly a prompt reply from DVLA re my licence situation it appears Pete was quite correct I salute you sir. So having read the below my old HGV 3 becomes a Class 2 Result! So medical D4 a D2 application then and a CPC. Standby all roads!! providing I get a job that is. Maybe a few hours refreshing wouldn’t go a miss.
Have you now got your new plastic licence with the correct categories?
I ask because I was/am in a similar situation but they won’t give me back my class 2.
Long story as short as I can make it…
Passed Class 2 in Dec '76 in Army.
Left Army '78.
Drove for a few years and then stopped, moved on to other things.
2 years ago returned to UK.
Passed medical, applied for licence, got sent a provisional Cat C.
Queried this, Got told that they had mo record of me passing the test and that I had to prove that I did.
Got in touch with Army Records. Got sent a doc with all (most) of my qualifications including the Class 2 that I passed.
Sent a jpg/scan of it to DVLA who then answered…
“While we now accept that you did pass your test in Dec '76, we decline to re-issue your entitlement because you failed to renew your old cardboard style licence for the new plastic style licence in '86.”
Ok, I’m paraphrasing a bit there. But that’s what they said.
Then I got a good paying job driving 7.5 puddlejumpers so wasn’t too bothered about chasing it up.
So I’d be interested to know how your situation pans out 
Hopefully, it’s a good result for you.