Two things will be known already - track and estimated speed at impact from the wreckage trail. There is a good possibility that altitude (but not height and track) could be established over the flight.
Given that he was higher than (almost) all the buildings, it's quite possible that recordings from the Heathrow 10cm radar will provide at least some information on his track in the peroid before the collision. Certainly that will be one area the AAIB are investigating.