That's the beauty of the Internet, Nigel---you can ask Michelob!

A substitute that has even less carbs - Take "magic zero carb
beer in concentrated form".  Pour a shot.  Dilute with water
until it has been un-concentrated back to the strength of beer.
You won't having any problem with the concentrated stuff.
Call it whiskey and you'll find it at all sorts of places.

Any chance you can drink less of a better beer?  Many real
ales in the UK are wonderfull.  A small portion ...

virtually all major supermarkets stock it

John