From Gov.uk:
Lighting requirements (113 to 116)
113
You MUST
ensure all sidelights and rear registration plate lights are lit between sunset and sunrise
use headlights at night, except on a road which has lit street lighting. These roads are generally restricted to a speed limit of 30 mph (48 km/h) unless otherwise specified
use headlights when visibility is seriously reduced (see Rule 226).
Night (the hours of darkness) is defined as the period between half an hour after sunset and half an hour before sunrise).
Laws RVLR regs 3, 24, & 25, (In Scotland - RTRA 1984 sect 82 (as amended by NRSWA, para 59 of sched 8))
Therefore in built up areas, 30mph limit, with street lighting it is not necessary to use dipped headlights or those infernal 'driving' lights.