More than half of all mortgages taken out during the past four years would have been barred if proposed new lending regulations had been in force, a trade body has warned.
The Council of Mortgage Lenders said 3.8 million credit-worthy borrowers would have been unable to get a mortgage between the second quarter of 2005 and the first quarter of 2009 if the Financial Services Authority's affordability rules had been in place.
Overall, it estimates that 51% of all mortgages written during the period would have been affected by the tighter lending criteria banks and building societies may be forced to adopt under the Mortgage Market Review.
The group has already warned that the proposed rules on mortgage lending will lead to house price falls and create "mortgage prisoners" who are unable to remortgage when their current deal expires.
Its latest research shows that around 16% of mortgages taken out between 2005 and 2009 would not have gone ahead if borrowers had been restricted to spending no more than 35% of their post-tax income on repayments.
A further 16% of people would have been barred by rules stating that lenders must assess affordability on the basis of a 25-year repayment mortgage, even if the mortgage term is longer than this or it is an interest-only loan.
Another fifth of mortgages were likely to have been blocked if lenders had had to assess affordability not just on the rate the borrower was applying for, but also on one that was 2% higher.
The CML said that while the proposals would have reduced the number of arrears cases by around 151,000 and repossession ones by 38,000, 3.8 million people who had never suffered repayment problems would not have been given mortgages.
It added that the impact of the measures would have fallen most heavily on first-time buyers, with 730,000 people who have not gone on to have problems keeping up with their repayments kept off the property ladder.
Around 80% of people with impaired credit histories who took out a mortgage during the period were also likely to have been excluded under the new rules, although the CML said around 20% of these people had run into payment difficulties in 2009.