A bank clerk who allowed fraudsters to access to his branch’s computers and attempt a £1 million scam has been jailed for four years.

Hans Patterson-Mensah, of Harlech Road, Cranford, led an unknown crook into a customer interview room at Natwest in Staines High Street in September 2012.

Once inside, the man inserted a device known as a KVM switch into a computer, giving the criminals access to the bank’s internal systems.

The fraudsters than fiddled the system to make it look like selected customers had paid large sums into their accounts, totalling nearly £1.1m.

The crooks had instant access to that cash but bank staff spotted the scam in their end-of-day audit and were able to recover all but £6,000 of the money.

An investigation by the Dedicated Cheque and Plastic Crime Unit (DCPCU) identified 24-year-old Patterson-Mensah leading a man into an interview room in 2012, on both September 8 and August 24, with the earlier occasion believed to be a test run for the actual attack.

Patterson-Mensah was convicted at the Old Bailey of fraud by abuse of a position of trust and was today sentenced at the Old Bailey to four years imprisonment.

DCI Dave Carter, head of the DCPCU, said: “This is a particularly serious crime because it involves a person in a position of trust abusing the faith placed in him to give fraudsters access to large sums of money.

“The vigilance of his co-workers at the bank ensured he did not succeed, and I am pleased the gravity of the offence has been recognised with a custodial sentence – reflecting the importance of protecting customers’ funds.”

The DCPU is a specialist police unit sponsored by the banking industry through Financial Fraud Action UK.

The unit helped secure 48 convictions and claims to have saved an estimated £440 million in reduced fraud activity since being established in April 2002.