@swansonj
How about this ?
http://www.legislation.gov.uk/uksi/1989/1796/schedule/3/made
1. A dim-dip device fitted to satisfy regulation 18 shall cause light to be emitted from the dipped-beam filament of each obligatory dipped-beam headlamp, each such light having, so far as is practicable, an intensity of between 10 and 20 per cent of the intensity of the normal dipped beam.
2. Running lamps fitted to satisfy regulation 18 shall be in the form of a matched pair of front lamps, each of which–
(a)is fitted in a position in which an obligatory front position lamp may lawfully be fitted, and
(b)is capable of emitting white light to the front having an intensity of not less than 200 candelas, measured from directly in front of the centre of the lamp in a direction parallel to the longitudinal axis of the vehicle, and of not more than 800 candelas in any direction.
"3. The electrical connections to the obligatory dim-dip device or running lamps, as the case may be, shall be such that the light output specified in paragraph 1 or 2 above is emitted automatically whenever–
(a)the engine of the vehicle is running, or the key or devices which control the starting or stopping of the engine are in the normal position for driving the vehicle, and
(i)the obligatory position lamps, but not the headlamps, of the vehicle are switched on, or
(ii)the obligatory position lamps are switched off."
Intrigued but not yet convinced!
Firstly, those seem to be the 1989 Regulations as made in 1989, so apparently do not reflect the present position.
Secondly, if you just look at Schedule 3, you would conclude that ALL cars (registered after 1987) are required to have running lights, and were thus required in 1989, which is and was clearly not correct.
I suspect the explanation lies in column 3 of schedule 1, which gives the exception from the UK Regs if you meet the relevant EC (as then was) regs. It may be that the relevant EU Regs get you to the same place. I don't know and don't think I've got the energy to trace it all through myself ... but if someone else does, I'd be fascinated to hear the result, and if necessary, I will re-enable my DRLs.
(I have a hunch the schedule you quote was the UK's attempt to make dim-dip compulsory, a requirement which was struck down by the EC. And interestingly, the point about dim-dip was a recognition that dipped headlights were TOO BRIGHT for street lit roads after dark. )
Edit: the Highway Code, I think, makes no mention of any requirement for DRL.
Further edit ... because I really wish I'd never embarked on this and don't want to sidetrack the main thread further with a new post: Glenn, I think I agree with you that the RVLR regs 1989 do indeed require DRL. I intend, against my will, to switch ours back on. But my puzzlement remains that they seem to require DLR or dim-dip for ALL cars, not just post-2011 type approvals. Yet the majority of cars in UK roads have neither.