I'll highlight this again...
A commonly given clearance when routing to Battersea Heliport from the north (e.g. from Elstree!) is to fly in a straight line from Alexandra Palace to Vauxhall Bridge, not above 1,000 feet London QNH, VFR.
When following this route, aircraft arrive at 90 degrees to the river Thames at Vauxhall Bridge, which is a compulsory VRP. The river is less than 300 metres or so in width at that point so a very sharp turn to starboard is needed to join heli-route H4 there, unless you fly a little bit further east and put a radius on the turn.
On reaching the river and reporting at Vauxhall, pilots are told to call Battersea Tower for onward clearance because it's the boundary of their ATZ.
The AAIB will of course already know which route the aircraft was flying on the day and what clearance was given.