John Woodhatch, 58, was sentenced to five years in prison and Adrian Taylor, 44, six years in prison after both pleading guilty to charges of money laundering following an investigation by the City of London Police.

The co-conspirators contacted the Guernsey Treasury in June 2012 claiming to be from Lagan Construction, which is currently carrying out a £50m project at the airport.

The pair told public officials they wanted to change the bank account details into which the Treasury was making its monthly payments to the company.

Once this was agreed and the latest monthly payment of £2.6m had been transferred into the new RBS account Woodhatch, who was working as a City broker, immediately instructed the bank to move the funds to accounts in Dubai and Turkey.

Woodhatch, from Epping, Essex, told RBS that the transfers were mainly to pay for a horse in Dubai.

But the RBS money laundering team were not convinced and referred the matter to the City of London Police for investigation in July 2012. They were later assisted by Guernsey Police.

Within a matter of days detectives had arrested Woodhatch and searched his home and commercial addresses.

A detailed review of the accounts found that £52,000 of the stolen funds had been transferred to Adrian Taylor, from Swanley, Kent.

He was arrested in October 2012 after handing himself into the City of London Police.

Detective Inspector Rob Stirling, who led the investigation for the City of London Police, said: “Woodhatch and Taylor thought they were too smart to be caught and would be left free to spend the £2.6 million stolen from the States of Guernsey.

“Unfortunately for them the City of London Police specialises in investigating cases of financial fraud and bringing those responsible to justice.

“Woodhatch and Taylor’s scam should also serve as a warning to other public and private sector bodies that could easily be targeted by fraudsters in the same way.”