On top of this, Mr Cook estimated that the rate on a 99pc mortgage could be around 0.5 percentage points higher than a typical loan.
In London, where high house prices in proportion to earnings mean first-time buyers normally purchase with 69pc mortgages, the extra cost would be even bigger.
Purchasing with a 99pc mortgage would cost a first-time buyer 53pc more than if they bought using a typical loan, Mr Cook said. This would cost them an extra £868 per month, and would bring their total annual mortgage bill to more than £30,000.
He added: “In London it would have been ridiculous. Your average first-time buyer mortgage there is already capped by the amount people can borrow relative to their income. It would have really struggled to gain traction.”
The plans for 99pc mortgages would have involved a revamp of the Government’s 95pc Mortgage Guarantee Scheme, which was introduced in 2021 in a bid to boost low deposit lending, after lenders withdrew these deals during the pandemic.
However, uptake of the scheme has been small. In the year to September 2023, it supported just 11,000 home purchases, equivalent to 1pc of all transactions.
A HM Treasury spokesman said: “We aren’t in a position to speculate about Budget measures. The existing scheme providing a 95% loan to value mortgage was introduced in April 2021, has so far enabled over 39,000 households to buy a home – over 86% of which are first time buyers.
“At the Autumn Statement the scheme was extended for a further two years to provide additional support for first time buyers.”
