Whitehall sources say information has emerged that MH17 crash evidence was deliberately tampered with, as the plane's black boxes arrive in the UK.
The sources said this included moving bodies and scattering the parts of other aircraft among the wreckage of the downed Malaysia Airlines plane.
The Air Accidents Investigation Branch in Farnborough has received the flight voice and data recorders for analysis.
All 298 people on board were killed in the crash in Ukraine on 17 July.
They included 10 Britons on the flight from Amsterdam to Kuala Lumpur.
Missile launch
Whitehall sources also told the BBC that pro-Russian rebels are believed to have discussed plans to hand MH17's two black box flight recorders to Russia.
It is understood that some of these conversations were intercepted by Ukrainian intelligence; the information is considered to be "very persuasive".
Intelligence has also been obtained which strongly indicates that the plane was shot down by an SA-11 BUK missile launched from a separatist-held area in eastern Ukraine.
British accident investigators are attempting to retrieve data from the recorders following a request by authorities in the Netherlands.
The Dutch Safety Board, which is leading the investigation, said "valid data" had been downloaded from MH17's cockpit voice recorder (CVR) which will be "further analysed".
The board said: "The CVR was damaged but the memory module was intact. Furthermore no evidence or indications of manipulation of the CVR was found."
Investigators will examine the other black box, the flight data recorder (FDR), on Thursday.