Detective chief inspector Craig Mullish of the City of London Police said: “We have seen criminals try to defraud customers of a number of leading energy companies by offering cut-price deals to those who use prepayment meters.

“These fraudsters approach victims on their doorstep and offer them cloned keys to top up their energy credit. Although the victim believes they have got a bargain, in reality they will end up paying for the energy twice.

“Energy companies can detect that they have not received payment for energy used and so the victim will be required to cover the costs.” It is understood customers of EDF Energy, E.On, British Gas, SSE and Scottish Power have all been targeted by the scam.

He added: “The perpetrators are believed to have links to serious and organised criminal activity, meaning that the money will be used to fund further criminal activity.”

The surge in fraud follows a similar boom during the pandemic, when scammers preyed on locked down and isolated households to dupe them out of huge sums of money.

Last year fraudulent delivery texts, fake Covid testing scams and swindlers pretending to offer help under government support schemes were common. The number of fraud cases reported to Victim Support, a charity that supports those affected by crime, doubled during the Covid crisis.

Diana Fawcett from Victim Support said: “We consistently see fraudsters using calculated and manipulative tactics to target people when they’re at their most vulnerable.”