You do not need an IMC rating or IR to fly IFR in the UK (at night or any other time). However, if you don't have one of those ratings, you must not fly in IMC.
Very true, but restrictions may apply to aircraft on foreign registrations. (I mention this because worldpilots location is given as Germany).
Irish registered aircraft for example can only be flown under IFR by the holder of an instrument rating (even in VMC).
dp