Have to disagree with you, Crab.
Rule 30 states "....in order to comply with the Instrument Flight Rules, an aircraft when in level flight above 3000 feet above mean sea level ......". It does not say you have to be above 3,000 ft to comply with IFR. . The sub-para (2) to which you refer allows ATC to modify your flight level or allow you to fly a hold without sticking to the usual FL as stated in the table to Rule 30 which I have not reproduced.
If what you say is correct, how do non-IR helicopter pilots fly around the Heathrow Zone at night? Flying at 3,000 ft and above would put them into the London TMA Class A airspace.