Tom Espiner is a business reporter.
When the next cap takes effect in October, people have been warned to expect a huge rise in energy bills.
Cornwall Insight says this could add another 630 a year to a typical bill.
Government support for those struggling to pay has been called for after the expected rise in bills.
The war in Ukraine has had an effect on energy prices.
If accurate, the most up-to-date prediction from Cornwall Insight would push annual energy bills for a household using a typical amount of gas and electricity to up to $2,500 from October.
The bill is expected to fall back to the current level in the summer of 2023.
Bill Bullen, the boss of Utilita, warned that elderly people and children were at risk because of a lack of heating.
We are going to see an extra 500 or 600 added to bills in October, and the chancellor will have to fund that for low-income households.
He won't be able to take this problem away for everyone, but for customers who can't respond to a price increase, that's where help needs to be targeted
The warning comes on top of a huge rise in what energy suppliers can charge customers. 18 million households will be affected by the 693 year rise in a typical energy bill, with 4.5 million customers on prepayment meters facing an even bigger increase.
Council tax, water bills and car tax all go up for some on 1 April.
Some financial support from the government is partially offsetting the blow of minimum wage rates rising.
The sudden increase in the cost of energy is the most significant for individuals, as prices in general are rising at their fastest rate in 30 years.
Four in 10 bill-payers have found it difficult to afford their energy costs, according to new official figures.
Andrew Bailey, the governor of the Bank of England, said the country is facing the biggest shock from energy prices since the 1970s.
It is the largest increase since the price cap was introduced.
Every six months the cap is set for England. Domestic customers in Wales and Scotland are protected from the fluctuations of wholesale energy prices.
Chris O&Shea, chief executive of Centrica, which owns British Gas, said his company was giving grants to those most in need.
We would love to do more. He told the Big Green Money Show that the market has gone through a change for a retail energy company.
He accepted that profits had risen sharply for the heavily taxed exploration arm of the business.
The Office for National Statistics said that people with low incomes, parents, people with disabilities, unemployed people and divorcees were least able to afford a bill shock.
The government has said that it is takingdecisive action to help people with the cost of living, including a 200 reduction to energy bills in October.
Sir Keir Starmer, the leader of the Labour party, said that the government's response waspathetic.
He said the government forced people to choose between heating their homes or eating.
He said that the Labour party would impose a windfall tax on the profits of oil and gas companies and use the money to help people with rising energy bills.
Chancellor Sunak told the Newscast that he was confident in what he had done. I know it is hard for people. We are facing a very difficult situation with the price of things going up and I want to do what we can to alleviate some of that, but I am also honest with people that we can not fix all of it.
Are you affected by this story?