Found it; goes on a bit but worth knowing:
http://www.legislation.gov.uk/ukpga/...0030020_en.pdf
Railways and Transport Safety Act 2003
PART 5
AVIATION: ALCOHOL AND DRUGS
93 Prescribed limit
(1) A person commits an offence if—
(a) he performs an aviation function at a time when the proportion of
alcohol in his breath, blood or urine exceeds the prescribed limit, or
(b) he carries out an activity which is ancillary to an aviation function at a
time when the proportion of alcohol in his breath, blood or urine
exceeds the prescribed limit.
(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.
Railways and Transport Safety Act 2003 (c. 20)
Part 5 — Aviation: Alcohol and Drugs
41
(3) In relation to the aviation function specified in section 94(1)(h) the prescribed
limit is—
(a) in the case of breath, 35 microgrammes of alcohol in 100 millilitres,
(b) in the case of blood, 80 milligrammes of alcohol in 100 millilitres, and
(c) in the case of urine, 107 milligrammes of alcohol in 100 millilitres.
(4) The Secretary of State may make regulations amending subsection (2) or (3).
(5) Section 94 defines “aviation function” and “ancillary activity” for the purposes
of this Part.
94 Aviation functions
(1) For the purposes of this Part the following (and only the following) are aviation
functions—
(a) acting as a pilot of an aircraft during flight,
(b) acting as flight navigator of an aircraft during flight,
(c) acting as flight engineer of an aircraft during flight,
(d) acting as flight radio-telephony operator of an aircraft during flight,
(e) acting as a member of the cabin crew of an aircraft during flight,
(f) attending the flight deck of an aircraft during flight to give or supervise
training, to administer a test, to observe a period of practice or to
monitor or record the gaining of experience,
(g) acting as an air traffic controller in pursuance of a licence granted under
or by virtue of an enactment (other than a licence granted to a student),
and
(h) acting as a licensed aircraft maintenance engineer.
Interesting that it refers to 'during flight' . . . hmm.
From the ANO 2016:
Drunkenness in aircraft
242.—(1) A person must not enter any aircraft when drunk, or be drunk in any aircraft.
(2) A person must not, when acting as a member of the crew of any aircraft or being carried in any aircraft for the purpose of acting as a member of the crew, be under the influence of drink or a drug to such an extent as to impair their capacity so to act.
And that's it.
Don't make it easy, do they?