All helicopters flying within the London Control Zone are subject to minimum visibility rules. To minimise noise nuisance, pilots are told to fly as high as their air traffic control clearance and prevailing cloud conditions allow. Pilots are told to fly precise routes and avoid "corner cutting".
Above all, normal rules of the air mean pilots should not fly "closer than 500 feet to any person, vessel, vehicle or structure".
However, multi-engine helicopters are given more scope to fly away from the designated helicopter routes with air traffic control clearance. The Agusta 109, the model reported to have crashed, is a twin-engine helicopter.
A notice to airmen was issued on 7 January warning of a 770ft crane erected in Vauxhall, lit at night, as an obstacle on the City routes and approach to Battersea heliport.
Whatever, turns out that the pilot was considered a first class aviator, and well liked by his colleagues. Also well known for his work with the air ambulances. So a very sad day for all concerned , thoughts to families and friends. R.I.P