Tax rises that kick in today will reduce what homeowners can borrow and potentially send house prices downwards, experts have warned.

The increase in National Insurance contributions will change how lenders run “mortgage affordability assessments”, a leading banker has warned. The assessments look at take home pay and test how much a worker can afford. The rising cost of living will also cut back what banks are willing to lend.

Charles Roe, of UK Finance, a banking trade body, told Telegraph Money the tax rise would immediately hit borrowing power. He said: “The increased cost of living – including changes to National Insurance payments – will reduce a borrower’s disposable income which could affect the amount they are able to borrow.”

Mortgage brokers and banks also sounded the alarm and warned sellers would have to cut asking prices when buyers were only given smaller loans.

Jonathan Harris, of mortgage broker Forensic Property Finance, said: “Market forces will come into play and sellers need to be prepared to negotiate in order to cover the cost if borrowers can’t raise as big a mortgage as before.”

Chris Sykes, of mortgage broker Private Finance, warned the housing market could be “crippled” if banks did not become more lenient and lend higher multiples of the lower salaries to cover the difference.

However, Ben Merritt, of Yorkshire Building Society, said the lender had already factored in the rise in tax. “Increased outgoings are likely to affect the amount buyers can borrow. It’s important we respond to the ever-changing landscape to make sure it best reflects homeowners’ ability to repay their mortgage,” he added