Although the 1963 Great Train Robbery, which made anti-heroes of Ronnie Biggs, Buster Edwards and their gang of villains, may be the most famous railway heist - it was certainly not the first.

Way back in 1855 a boat train from London to Folkestone was targeted by crooks who made off with gold worth more than £1.3 million in today's money. Reporter Rhys Griffiths takes up this tale of greed, desperation and betrayal...

The South Eastern Railway boat train thundered across Kent as night fell, bound for Folkestone Harbour and connection with the steamer service to Boulogne from where passengers, goods and mail would continue on to Paris.

On board was a precious cargo, gold bars to the value of £12,000 and a quantity of gold coins, which had been loaded at London Bridge by Chaplin & Co carriers in three sealed boxes.

Having completed their journey across northern France with the Chemin de Fer du Nord, the safes in which the boxes travelled were opened and their seals broken.

The gold was gone and in their place were bags of lead shot. An international manhunt was on.

The destitution of Fanny Kay

Edward Agar was a career criminal with a skill for safe-cracking. He has been widely acknowledged as the brains behind the heist on the night of May 15.

His fellow conspirators were William Tester and James Burgess, two employees of the South Eastern Railway, and William Pierce, a former SER worker who had been dismissed from the company because of his gambling.

Their robbery of the night mail had been meticulously planned, helped by the inside knowledge of the workings of the railway the men possessed.

Because of the nature of the crime - taking the haul of precious metal as it made its way between London and Paris - the investigation was international in scope and suspicion fell all along the route the bullion would have took.

Despite the involvement of law enforcement professionals on both sides of the Channel, it appeared the culprits would never be found.

That was all to change the moment Fanny Kay walked into the infamous Newgate Prison in the City of London and demanded to speak to the governor.

Kay, who herself had previous worked on the railway, was Agar's lover and mother of his child.

When Agar was convicted of fraud over forged cheques he was sentenced to life and was to be transported to the penal colonies of Australia, never again to set eyes on his young child.

While awaiting transportation in Pentonville Prison, Agar used his lawyer to ask his accomplice William Pierce to pass a significant amount of money on to Kay to help support her and the infant.

Pierce would come to regret his decision not to pass on the cash as promised. By the summer of 1856, destitute and desperate, Fanny Kay was ready to tell all.

Turning gold into lead

Beginning its journey in London, the bullion the gang targeted would have been packed into wooden boxes, weighed and sealed before being transferred to the awaiting boat train at London Bridge.

At the station they were placed inside travelling safes made of iron and secured with two locks. The keys were then entrusted to railway staff in London and Folkestone and also to the captain of the cross-channel steamer.

The audacious crime took months of planning, with members of the gang observing the precise operation by which the gold would be conveyed to Folkestone.

Although the theft itself was relatively straightforward - open the boxes, swap out the gold for lead shot, and reseal the containers - it did require access to the keys and ensuring Burgess was the guard on the night of the robbery.

Tester, who worked in the railway company's offices, was key. He ensured Burgess was aboard as the train pulled out of London Bridge, and helped Agar access safe keys.

Working fast as the train sped along the South Eastern mainline towards the coast, the gang methodically switched their booty for the bags of lead shot. Once the train arrived at the port they slipped from the guard's van and disappeared among the other passengers.

When the boxes arrived in Boulogne they were weighed and found to be light, but despite this they were conveyed to the French capital where they were opened and the scale of the crime became apparent.

A reward of £300 was offered for information leading to the apprehension of the thieves and detectives on both sides of the Channel were left chasing leads that never amounted to anything concrete.

For a year it looked as if the gang had successfully pulled off one of the greatest crimes of the fledgling railway age.

The conspiracy unravels

Fanny Kay told the police and the South Eastern Railway company everything. And her former lover Edward Agar - outraged by Pierce's treatment of the girl - corroborated her account.

Pierce, Tester and Burgess were brought in, and in January 1857 their trial was held at the Old Bailey amid a blaze of press interest in the sensational tale.

Agar's testimony, having turned Queen's evidence, was clear and convincing as he set out his role in the conspiracy.

It took the jury just minutes to find the three men guilty of larceny.

They had pulled off the most audacious plot, and in the process netted themselves a small fortune. All lost because of greed and a broken promise.