The men are currently in custody in connection with an allegation of conspiracy to steal from Barclays Bank, and conspiracy to defraud UK banks, says the Metropolitan Police's Central e-Crime Unit (PCeU).

The PCeU swooped yesterday and today following an investigation which began soon after the money was stolen from the Swiss Cottage branch of Barclays in April.

Police say that a gang member managed to connect a keyboard video mouse (KVM) device to a computer at the branch after gaining access by pretending to be an IT engineer.

The KVM device allowed the gang to control multiple computers, enabling them to transfer money to a series of predetermined bank accounts. Barclays has recovered a "significant amount" of the £1.3 million.

In a statement, the UK bank says: "We identified the fraud and acted swiftly to recover funds on the same day. We can confirm that no customers suffered financial loss as a result of this action."


A KVM device

The PCeU says that this technique is becoming increasingly popular with thieves. Last week 12 men were arrested in connection with a similar, albeit failed, attempt to steal from a Santander branch.

Police are now carrying out searches at several addresses, including what is thought to be the gang's operation control centre, seizing cash, jewellery, drugs, thousands of credit cards and personal data.

Detective Inspector Mark Raymond, PCeU, says: "Those responsible for this offence are significant players within a sophisticated and determined organised criminal network, who used considerable technical abilities and traditional criminal know-how to infiltrate and exploit secure banking systems."

Alex Grant, MD, fraud prevention, Barclays, says: said: "We have been working closely with the Metropolitan Police following a security breach at our Swiss Cottage branch in April 2013. We identified the fraud and acted swiftly to recover funds on the same day. We can confirm that no customers suffered financial loss as a result of this action."