Joseph Pyle, 56, of Morden, south London, will be sentenced later together with Frank Tyson, 62, of no fixed address, who acted as a courier in the deal involving class A drugs.
Peter Gillett, 32, described as a pop singer and bit part actor, was also convicted of taking part in a drugs deal. Gillett, of Burgess Hill, West Sussex, who claimed to have been 'adopted' by Reggie Kray, the gangster, while serving six years for armed robbery in Parkhurst prison, was found guilty of dealing in class A drugs.
Pyle masterminded two deals involving heroin and a heroin substitute worth an estimated pounds 300,000, the court was told. The three will be sentenced next month.
A fourth defendant, Terence Plummer, 55, a stuntman, of Leatherhead, Surrey, was acquitted of being involved in drug dealing.
Detectives from the South-east Regional Crime Squad drugs wing uncovered the deal after an informer was approached by Pyle and asked about buyers for heroin. An undercover detective moved in posing as a buyer and Pyle was kept under surveillance despite the fact he practised anti- surveillance measures designed to throw police off his trail.
The jury were told how the first deal to buy pounds 25,000 worth of heroin went wrong when one of Pyle's men could not open the boot of an unmarked police car in which the drug was supposed to be left.
Despite the failure Pyle was anxious to strike a deal with the undercover officer, named only as 'Dave' in court.
He offered to sell the officer thousands of ampoules of morphine sulphate and opium stolen from a Ministry of Defence consignment after the Gulf war. The drugs were used to relieve the pain of wounded soldiers.
Pyle arranged to meet 'Dave' at the Sheraton Skyline hotel, Heathrow, in July last year. Before the meeting he was seen by police surveillance officers meeting Gillett at Burgh Heath, in Surrey.
Switching surveillance to Gillett, police witnessed him driving to Brighton where he met Tyson. Both men then went to a lock-up garage where they were seen placing black plastic bags believed to contain the drugs into the car.
They drove to Heathrow where Pyle instructed them to leave it in the back of another unmarked police car. Pyle was paid pounds 14,000 and was arrested as he left the hotel room. Gillett and Tyson were arrested at a neighbouring hotel.
The convictions came at the end of two trials estimated to have cost nearly pounds 1m.
The first, at Southwark Crown Court, was aborted after three members of the jury said they had been offered money to return not guilty verdicts. When they refused they were threatened with violence. During the latest trial, jurors were given 24-hour police protection and armed police were in court.
As a result of the investigation detectives made the biggest police seizure of heroin in Britain: 40kg (88lbs), worth an estimated pounds 8m, were recovered from a warehouse in Wimbledon, south London, in August last year.
Detectives say they did not have enough evidence to link the haul to the defendants although the chemical composition is identical to that seized from a man working for Pyle when the first drug deal failed.