Uk Railways and Transport Safety Act 2003 can be found
here. Part 5 (section 93) is the aviation relevant part that states:
(2)The prescribed limit of alcohol is (subject to subsection (3))—
(a)in the case of breath, 9 microgrammes of alcohol in 100 millilitres,
(b)in the case of blood, 20 milligrammes of alcohol in 100 millilitres, and
(c)in the case of urine, 27 milligrammes of alcohol in 100 millilitres.
This is all 1/4 of the current UK drink/driving laws.