North Londoners are paying millions more than they should be on their energy bills, a survey has found.

According to the findings customers of the “big six” energy suppliers – British Gas, EDF Energy, nPower, E.On, Scottish Power and SSE – in three constituencies are among the worst five affected in the whole country.

The analysis shows annually people across Hornsey and Wood Green overpay by an estimated £9.3m while Holborn and St Pancras customers overpay a total of £9.04m and Hampstead and Kilburn customers must find £9.02m extra.

Per household this means Hornsey and Wood Green bill payers are paying £261 extra while Holborn and St Pancras and Hampstead and Kilburn customers are forking out £272 more.

This compares to the highest – the Isle of Wight where residents pay an estimated extra £10.7m per year or £261 per household.

The analysis comes in a week when Conservative backbencher John Penrose invited MPs to add their signatures to a letter urging the government to press ahead with energy price caps following Theresa May’s election pledge U-turn.

Confirming her intention to sign Mr Penrose’s letter, Catherine West said: “Fuel poverty is very serious in Hornsey and Wood Green. I’m very keen for the “big six” cabal to be broken.

“Anything alternative energy promoters can do to break the stranglehold is very welcome,” she added.

Tulip Siddiq MP said: “These figures are the latest reminder of our broken energy market. Only last year, the competition and markets authority found households have been paying £1.4 bn a year more for energy than they should.

“For too long, the big six have been allowed to make excessive profits.

“People want reliable, affordable energy and that is why I support calls for an immediate emergency price cap to ensure the average dual-fuel household energy bill remains below £1,000 per year,” she added.

Keir Starmer MP said: “People in Holborn and St Pancras need a Labour government so the whole market can be fundamentally reset, with new suppliers working to keep bills down.”

In response, an EDF spokesman said: “It’s important intervention helps build a fair and trusted market focused on helping those most in need.

“We keep prices under constant review and our tariffs reflect the costs we incur to supply customers with electricity and gas – many of which are out of our control – this in addition to a small margin, which allows us to invest.”

An SSE spokesman said the company had stated “consistently” that any intervention should be subject to consultation on both the principles and detail. It plans to argue strongly for competition, not caps.

A spokewoman said E.ON “constantly reviews its tariffs” and seeks ways “to keep prices as affordable as possible” including by boosting engagement in the energy market by its standard variable customers.

She added E.ON has been contacting “potentially vulnerable customers” with a personalised quote for a fixed one year tariff, as well as developing a programme to speak with customers.

Npower declined to comment.

To reach the figures the survey authors calculated the weighted average of the big six SVT rate paid by customers in each constituency, excluding prepayment meters.

Following this, they subtracted the average of the cheapest 10 tariffs in the region in which that constituency is based and then multiplied the answer by the number of households, excluding pre-paid meters, in each constituency (estimated as being 80pc of households).

The authors also took account of the £50 annual, averaged savings for the 20pc of households on pre-payment meters, a result of the pre-payment cap.

Explaining the motive behind its analysis, the founder of renewables firm Octopus Energy Greg Jackson said: “We welcome a more competitive environment where people can see what they’re paying and vote with their feet if they don’t like it.

“It’s better for customers, better for the market, and better for business,” he added.