A live hand grenade was found at a home following a raid by police investigating the suspected theft of £1million.

Four people were arrested after raids yesterday morning at an address in Bowes Road, Enfield, and another in Islington.

Detectives also seized more than £80,000 in cash from the raids as part of an investigation into the suspected theft of £1million from two UK banks.

The investigation, led by the Metropolitan Police’s new Cyber Crime Unit, started after bank customers alerted officers after they had inadvertently downloaded a virus onto their computer by opening emails claiming to be from their bank.

A total of £1million was taken from their bank accounts and transferred to a series of other accounts, from which it was then laundered.

Two 31-year-old men, a 27-year-old woman and a 24-year-old woman were arrested on suspicion of conspiracy to defraud, conspiracy to launder money, and possession of an explosive.

Detective chief inspector Jason Tunn of the Cyber Crime Unit said: “These arrests by the Met's Cyber Crime Unit follow an investigation into what we suspect is an international and organised crime targeting a number of bank customers in London and across the UK.

“The victims have been hoodwinked by malware-carrying emails purporting to be from their banks, and subsequently had money taken from their accounts.

“The Met's Cyber Crime Unit is determined to protect people and businesses in London from cyber crime, which can see businesses ruined and people’s hard-earned money taken from them in a second. We are working closely the banking industry to achieve that.

“We will also seek to restrain and seize criminal profits where possible, in order to remove the financial benefit of online crime from cyber criminals."