The energy regulator confirmed an 80% rise, sending the average household’s yearly bill from £1,971 to £3,549 from October.
Factors for the prices going up include supply and demand following a particularly cold winter across Europe in 2020.
Mayor Khan is also calling for the introduction of a lifeline tariff for the most vulnerable Londoners, providing the minimum energy needed for a household to function for free.
Charges would kick in only once a minimum use threshold had been met.
City Hall says this would help ensure “people would not need to choose between heating and eating this winter”.
Price cap announcements will become quarterly after today’s announcement, with the October cap running until 31 December.
It is feared that this energy price cap hike would plunge a third of the population into the same position.
The mayor said: “Ofgem’s announcement that the energy price cap will rise to £3549 in October confirms what many of us have long feared.
“Despite repeated warnings, the government has consistently failed to intervene and Ministers must act now to prevent this cost of living crisis becoming a national disaster.
“Without government support, some Londoners will not only be forced to choose between heating or eating but could struggle to do either.
“The government must immediately freeze bills and introduce a Lifeline Tariff to ensure the most vulnerable people in our city receive a basic amount of free energy every day.
“Through transformative initiatives like my Warmer Homes scheme I’m committed to doing all I can to support Londoners through this deepening crisis but, with energy prices soaring and more families struggling to make ends meet, this government needs to step up and take urgent action now.”
A government spokesperson said: “We know people are incredibly worried about rising energy bills, following unprecedented gas prices across the continent driven by global events, including Putin’s aggression in Ukraine and his weaponization of energy in Europe.
“Direct support will continue to reach people’s pockets in the weeks and months ahead, targeted at those who need it most like low-incomes households, pensioners and those with disabilities.
“As part of our £37 billion package of help for households, one in four of all UK households will see £1,200 extra support, provided in instalments across the year, and everyone will receive a £400 discount on their energy bills over winter.
“The civil service is also making the appropriate preparations in order to ensure that any additional support or commitments on cost of living can be delivered as quickly as possible when the new Prime Minister is in place.”