Households face a “plain grim” outlook as higher energy bills and petrol prices force them to find at least GBP442 extra to get through the winter, according to an analysis.

While Boris Johnson used his conference speech to trumpet the UK’s future as a high-wage, high-skilled economy, Kevin Brown, a savings expert at the investment firm Scottish Friendly, accused the prime minister of failing to account for an “alarmingly fast-paced cost of living crisis”.

“Our own analysis estimates that households are already swallowing at least GBP442 worth of energy and petrol price rises on average this winter,” he said.

If the petrol price surpasses GBP1.60 a litre – it is currently at an eight-year high of 138p amid predictions of hitting an all-time high by Christmas – the report said an individual would need to find an extra GBP700 to cover their energy and fuel costs or more than GBP1,200 if a couple both drove to work.

Petrol and energy costs make up about 40% of official headline inflation figure which climbed to 3.2% in August, the highest level for nearly a decade. “This is, in short, totally unsustainable,” Brown said. “Wage increases are well and good, but if the cost of living is surging at the same time, then any of those gains will be wiped out.”

From next year workers will also be squeezed by a national insurance rise that will add at least another GBP254 to the tax bill of a median wage earner. Ahead of the budget on 27 October analysts said taxpayers would be looking to the chancellor for help.

“As it stands, the Bank of England and prime minister are washing their hands of the issue, and the outlook for the rest of us is just plain grim,” said Brown.

A separate report echoed the growing concern about rising living costs. In September, 27% of people polled by the insurer LV= said rising prices were a worry, up from 24% in June. Nearly two-fifths said their outgoings had already increased while about a fifth are saving less, the survey of 4,000 people found.

The quarterly barometer showed consumer sentiment had deteriorated over the past three months but remained above last year’s low, said the LV= managing director of savings and retirement, Clive Bolton. “We are in a period of adjustment as life slowly begins to return to normal after Covid and the reality of living in this new environment is beginning to bite.”