They worked for European cash-handling company Loomis and stole 26 bags of cash on March 14 this year. The "audacious" robbery involving cash belonging to Credit Suisse bank, which has never been recovered, took place near a cargo depot at Heathrow Airport and was described in court as being akin to a Hollywood script that could be titled 'The Heathrow Heist'.
"You Siddique and Singh played your parts to perfection. You had been involved for a considerable period in the planning," said Judge Stephen John during sentencing.
A third man, named Rafaqat Hussain, was jailed for 10 years and three months as the mastermind of the raid which was branded as a "classic inside job".
"You were an organiser, trying to keep your involvement at a distance. No doubt there were others in the plot as yet unidentified, but you were the principle, expecting a large slice of the proceeds and above Siddique and Singh in the hierarchy," the judge told Hussain.
The court was told that after driving from the depot, Singh and Siddique reported their van missing. Siddique was later found bound by cables on a service road near M40 highway in Buckinghamshire, with the van abandoned and the cash missing.
The two security guards pretended to be victims of a raid, but phone records showed Siddique had been in contact with Hussain and Singh.
Secret recordings made by a device planted by police in Hussain's car caught him admitting he had all the cash and boasting that he could buy any car he wanted with it. Both Singh and Siddique had previously denied one count of conspiracy to steal, but the jury found them guilty at the end of a trial.
Hussain had pleaded guilty to conspiracy to steal, money launder and commit burglary. He had arranged to buy a house in Buckinghamshire with the stolen cash, the court was told. The mastermind wept in the dock as his barrister, Bairaj Bhatia, said he had "failed his family" by carrying out a crime.