I can not see how the pilot could have been legally VFR in those conditions of freezing fog with such poor visibility. You have to be VFR to fly in or around Battersea Heliport, unless the helicopter is twin engined, IFR equipped, with the pilot IFR qualified and flying above the minimum safe altitude. Battersea Heliport would not have an IFR approach for the pilot to descend below the MSA.