You might want to read this before telling us the law no longer is in force.
Unless any part of 1872 Licensing Act has been superseded since August 2009, some of it remains in force.
The law still creates an offence of being drunk in public and of being drunk in charge of a carriage – since reinterpreted to include bicycles.
The crime has a maximum penalty of £200 or 51 weeks.
Personally, consuming alcohol (and who said just one drink?) and venturing out onto the public highways is just plain stupid. Who are we to say that, on the back of a 8-12hr night shift, he's not consumed 1/4 of a bottle in one measure. Perspective, please!
I'm fervently anti drink driving, so being asked if it's OK to have a drink before a bike ride, I'd be inclined to say "No".
Employees and the general public in general are very intolerant of alcohol and being in control of a moving vehicle. Period.