Under Section 1a of Schedule 5 (when flying under Instrument Flight Rules within controlled airspace) it adds this interesting footnote:
*Unless the appropriate air traffic control unit otherwise permits in relation to the particular flight and provided that the aircraft
complies with any instructions which the air traffic control unit may give in the particular case.
So if you ask your ATC unit to fly IFR (not IMC) in their airspace without an ADF it is in their power to say yes or no. Anyone tried this?