Lemain
Not sure from your profile if you are a helicopter pilot.
I read through this thread start to finish. Much better information / speculation on the Rotorheads thread, though there is some "tosh" there also. Some of the speculation here is not relevant to helicopter operation, or to helicopters in the London Zone, or to a twin helicopter (not a single) in that environment.
To sumerize, the flight was from Redhill to Elstree 1 POB. Working Heathrow Special, entered the zone. Being a twin, helirouts are not mandatory. Elstree was not possible due to deteriorating weather so RTB requested, as Redhill remained clear. On the way back, asked HRS for a divert to Battersea - (speculation) weather closed in on him? Diversion cleared with Battersea by HRS and given. No radio contact made with Battersea and the rest is on the news.