As Ethel said you contact the DVLA -you might have to undertake a medical to show that you dont have an ongoing problem with alcohol -I know thats what they do nowadays before your license is 'returned'.
Yeah -obviously I dont condone drink driving at all but a lot of people think you are stopped because of erratic driving but it could be something like a faulty taillight which gives them the excuse to stop you.
However all that said in Scotland the Police can now pull you over without reason -good thing in my books.
As far as I know the Police have alaways had the ability to stop anyone provided they have "reasonable cause".
There was a big stink around that time over the way drink drive samples were examined, this resulted in 1000s of bans being overturned.
Your license would have been the old pink paper one that would have expired when you reached 70, your license would not have been valid for those three years, but once the ban had finished you would have been able to ask for it back.
Now after all this time the system has changed to photocard licenses and the rules will be stricter but read thru this and it explains what you need to do:
http://www.direct.gov.uk/en/Motoring/DriverLicensi ng/EndorsementsAndDisqualifications/DG_4022491