Handy and SASless
Choice of VFR or IFR
22.—(1) Subject to paragraph (2) and to the provisions of rule 21 an aircraft shall always be flown in accordance with the Visual Flight Rules or the Instrument Flight Rules.
(2) In the United Kingdom an aircraft flying at night:
(a) outside a control zone shall be flown in accordance with the Instrument Flight Rules;
(b) in a control zone shall be flown in accordance with the Instrument Flight Rules unless it is flying on a special VFR flight.
So the only exception to IFR at night is Special VFR in a control zone - there is no get out, stated or implied for aircraft below 3000' - that only applies clear of cloud in sight of the surface during the day. Hence my comment that NVFR does not exist in UK for civil traffic.