The reference quoted by Jim59 (which is to SERA.5001) has not been revoked. Helicopters may still be permitted to operate under VFR in flight visibility of less than 5km down to a minimum of 800m. The critical phrase in the Regulation, however, is 'When so prescribed by the competent authority'. The UK has prescribed that VFR flights may be conducted in a visibility of not less than 1500m but has never prescribed the further decrease to 800m for helicopters. The current legal instrument for this prescription is ORS4 No.1067.