Homeowners in the so-called “blue wall” have seen their mortgage payments rise by around £3,000 a year since Liz Truss’s mini-budget, the Liberal Democrats have claimed.

The party says areas in southern England – which it will is targeting in the run-up to a general election expected next year – have been “hardest hit” by the increases.

Typical homeowners coming out of a two-year deal in the week after the mini-budget last September would have seen their rate shoot up from 1.69% to 5.17%, according to Lib Dem analysis of data provided by the House of Commons Library.

Those in London have seen their mortgage payments rise by an average of £3,066 and those in the South East by £2,944, the party says.This is compared with an average of £2,003 across the country, according to its analysis.

Chancellor Jeremy Hunt ruled out mortgage interest relief at source earlier this year over fears it would worsen inflation, instead agreeing measures with lenders aimed at easing the burden of repayments.

These included a 12-month grace period before repossessions begin for borrowers struggling with costs, and allowances to extend the term of their mortgage or move to an interest-only plan temporarily.

Ms Truss has defended her mini-budget and suggested it may have paid off in the long term, although the markets were spooked, the pound fell to a 37-year low and mortgage costs increased in its aftermath.

Lib Dem treasury spokeswoman Sarah Olney said: “One year on since the disastrous mini-budget, families are still facing a crippling Truss tax on their mortgages.

“Rishi Sunak has shown he is totally out of touch with families having to cut back because their mortgage payments have gone through the roof.

“He could choose to help struggling homeowners at risk of losing their home, instead he is handing billions of pounds of tax cuts to the banks.

“People will never forgive this Conservative government for taking a wrecking ball to the economy and then forcing families to pick up the tab.”