We've selected "Drunk in Charge" Fined £20 as our second Chance.
Under the Licensing Act 1872 (we learn from bikeforall.net's handy guide to cycling and the law) it is an offence to be drunk in charge of a bike. Just as it is an offence to be drunk in charge of a cow, and we certainly wouldn't condone such drink-driving. But it seems the law is never enforced.
More recently, the Road Traffic Act of 1988 makes it illegal to cycle on a road or in a public place if 'unfit to ride... that is... incapable of having proper control' though drink or drugs.
You can't be breathalysed or asked for a sample, any more than a pedestrian or horse can. So - as long you have proper control of your bike - you can enjoy a drink or two and cycle home.
Combination locks can be useful here. If you're too drunk to remember the combination, or to be able to work the fiddly barrels, you're not fit to be cycling anyway.
Meanwhile, I'm (a) off soon to cycle in Poland, where the penalties for drunk cycling are somewhat bizzarely the same as for drunk driving - so better go by car if you're thinking of a heavy session, cycling could be dangerous with all those pissed drivers - and (b) going to set up a bar called Moderation, so that I can truthfully tell the doctor I only drink in Moderation.