The E&W limit is quite generous, equating to around 5 units consumed by a man of average weight, and back when beer was 3 to 3.5%, that was 2.5 pints. Beer is stronger now,for some unfathomable reason. Measures of spirits are also larger.
The BAC calculator linked above actually tells you how long you must wait to be clear of blood alcohol, not legal.
I would not expect a half of 5% plus a double to take a 13 stone man over the legal limit, but it will impair his driving. It's not a good idea but that wasn't the question.
I'm quite tempted to buy one of those Alcosense devices and experiment at home.