Documents recently released from the national archives have shed light on a gold bullion heist at Croydon Airport 75 years ago.

A group of notorious gangsters were involved in stealing the gold, worth an estimated £12million at today’s prices. It was never recovered.

In the 1930s, Imperial Airways transported freight, mail and gold bullion around the globe from the airport.

Security was very lax and with only one person on night duty and nothing but a set of keys keeping them from the strongroom, it was the perfect target for the ruthless robbers.

At 4am on March 6, 1935 three men walked unchallenged into the main airport building while Francis Johnson, the man on duty, woke up and made his way onto the air strip to receive a German airliner.

At 7am he would discover that they had strolled off with a fortune in gold bound for Paris and Brussels.

The gold was never found and despite at least five strong suspects, only one person went to jail for the theft.

Cecil Swanland, a 47-year-old impoverished artist with expensive tastes and a young, stylish wife, was jailed for seven years in connection with the crime.

The other two men charged - Silvio ‘Shonk’ Mazzarda, a 38 year-old bookmaker and prominent member of the notorious Sabini gang and a man in his 70s called John O’Brien - were cleared.

Mazzarda, O’Brien and another man known only as Little Harry were involved in the actual robbery. They were picked up by taxi driver George Mason and driven to the airport to pick up the gold and then taken to Swanland’s house.

If it was not for a cyclist who had taken down the number of the taxi when he saw it by the airport at 5am, the men might never have been caught.

The taxi number led the police to Mason who said that he had been woken up by someone called Little Harry, who they never identified, asking him to drive some men to Croydon Airport from Kings Cross Station.

Mason said that he had known Shonk Mazzarda for 30 years and identified him and O’Brien in an identity parade.

In court, however, he changed his testimony and refused to acknowledge that he knew the men.

As a result they could not be prosecuted and walked away.

According to the released files, the police interviewed Mazzarda again in 1937 and he told them that they had obtained copies of the strongroom keys from Burtwell Peters the chief unloader at the airport. He was paid handsomely for his part in the crime.

It is unknown why Mazzarda felt comfortable talking to the police.

It could be that the getaway driver for the Sabini gang was so confident of his strong mob connections that he was not too worried about being arrested.

Swanland was not so lucky. His nosy landlady Mrs Schultz was able to testify that she had seen a taxi arrive at his house and men unloading boxes early in the morning of March 6.

When the police searched Swanland’s house they found newspaper reports of the theft, an Imperial Airways timetable and debris in the fire place which turned out to be an iron band similar to those securing the boxes of gold.

In the dustbin they found seals for Messrs Japhet & Co, exactly like the ones that had been on one of the missing boxes.

Swanland, who had previously served two substantial prison sentences for forgery and three for theft, was unable to explain why he had ordered £59 worth of clothes, bought a pair of gold cufflinks and a £50 brooch for his 21-year-old wife before the trial, despite having no money.

Evicted from her lodgings, Mrs Swanland moved in with her mother who lived at 48 Dean Street. Although it was never mentioned in court, the police believed that the gold had been transported to this address.

Mrs Swanland, who had no form of income yet, was known to have a substantial bank account after the robbery. She made applications to leave £30 at Wandsworth prison for her caged lover.

For his part, Swanland had to spend seven years locked up before he could enjoy the proceeds of the crime.