Police have seized a number of items from an address in Brent following the arrest of eight men in connection with a £1.3 million theft from Barclays Bank.

The theft is believed to have occurred after a gang took control of the computer system in the bank’s branch in Swiss Cottage.

The men, who are aged between 24 and 47, have been questioned in connection with an allegation of conspiracy to steal from Barclays Bank, and conspiracy to defraud UK banks. They are in custody in London police stations.

Cash, jewellery, drugs, thousands of credit cards and personal data have been seized in searches at addresses in the borough and Westminster, Newham, Camden, and Essex.

Detectives described one of the addresses in central London as the fraudsters’ control centre.

A search of branch in Finchley Road, where £1.3 million was stolen in April, unearthed a “keyboard video mouse” (KVM) switch attached to a 3G router to one of the computers. A KVM switch would allow the fraudsters to transmit desktop content.

It is alleged one of the plotters posed as an engineer, saying he was there to fix computers.

The KVM could allow someone to control a number of computers.

It is believed the gang could have been using the gadget to transfer money remotely into different bank accounts.

DI Mark Raymond, investigating officer, said: “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.”

“Organisations need to have proper physical security in place and foster an attitude so staff can challenge people and say ‘Where is your pass?’.

“It is not just money that could be stolen, but also data.”

The Barclays theft is being dealt with by the same investigation team that is dealing with the Santander attempted robbery, as part of the same police operation.

Police believe the gang that targeted Barclays had a “control room” in Seymour Place, Marylebone, central London.

Detective Superintendent Terry Wilson said he believes that one of the men who is under arrest is the “Mr Big” of UK cyber crime.