The British lawyer for a Russian oil firm and his pilot who died in a helicopter crash 14 years ago were murdered by Russians, a friend today claimed.
Stephen Curtis, 45, and Max Radford were killed when their helicopter crashed near Bournemouth Airport in Dorset in March 2004.
Mr Curtis was said to have had links with the late Boris Berezovsky, who was exiled in Britain after falling out with Vladimir Putin, and had received death threats and had his phones tapped before his death.
Despite conspiracy theories surrounding the crash and a coroner stating the case had all the hallmarks of an 'espionage thriller', verdicts of accidental deaths were given at the two men's inquest. It was heard that pilot error was to blame.
But John Hackney, a fellow pilot and friend of Mr Radford, has spoken out in the wake of the nerve agent attack on a former Russian spy in Salisbury, to raise questions over the fatal crash.
Mr Hackney said he would welcome the case being investigated again and would do anything to clear Mr Radford's name.
Mr Hackney, 81, said: 'Those of us who knew Max and knew aviation always felt he must have been shot down. We can't say for sure, but we suspected foul play.
'The day of the funeral we were all still talking about it and all of us said exactly the same thing - "this is not an accident". We all said to his dad "as long as we live we shall never ever believe this story".'
Mr Curtis had been the managing director of the Menatep group which had a controlling stake in Yukos Oil.
He had offices in London's Mayfair and lived with his wife Sarah and his then 13-year-old daughter Louise at a 19th century castle on the Isle of Portland, Dorset.
A week before the fatal crash Curtis told a friend: 'If anything happens to me in the next few weeks, it will not be an accident.'
On the evening of March 3, 2004, he boarded his private Augusta A109E helicopter at Battersea Heliport being flown by Mr Radford.
The weather on the flight to Bournemouth deteriorated and the helicopter came down on the approach to the airport.
The official investigation by the AAIB (Air Accidents Investigation Branch) found no evidence of sabotage and stated Mr Radford must have become disorientated when the weather worsened.
Mr Hackney, from Ringwood, Hampshire, said: 'I saw Max the morning of the accident. He had got this lovely new helicopter, it was a very nice piece of kit with all the latest navigational aids.
'He said he was going to pick up a guy in London and I set off on my day and then on the way back in the evening I heard about the accident.
'It was just unbelievable. Where it happened, he was only a mile away from the landing site, the weather was not that significant and he could see where he was going.'
Mr Hackney added: 'He had done a lot of flying, he was very experienced and it was a trip he had done so many times.
'Those sort of helicopters don't go bang and just drop. The odds of it happening like that are so rare.
'That's the way Russia operates. In 2004 we weren't so aware of those kind of tactics as we are now. I still don't believe it was pilot error and I would welcome any re-investigation.'
Sir Christopher Chope, the Conservative MP for Christchurch, Dorset, said he had always been sceptical about the conclusion of the case too.
He said: 'I was always sceptical about the official verdict on it but looking at these things the best assassins are the ones who cover their tracks.
'Whether it could be the state or mafia groups or whoever, how can we prove it if you haven't got the evidence?'
Yvette Cooper, chairman of the House of Commons home affairs select committee, has called for a review into 14 deaths where Russian involvement was suspected.