Abbey, Britain's second largest mortgage lender, has increased the amount it will typically lend borrowers to up to five times income, to help ailing first-time buyers.
The move is in response to the relentless rise of house prices but some experts believe such large loans could lead borrowers into repayment difficulties, especially with interest rates expected to edge upwards in the next few months.
Abbey said it would increase its standard income multiple - the amount it will generally lend home-buyers - from a previous 4.5 times salary.
Individuals or couples with a 25 per cent deposit and an annual income of £50,000 sterling or more will be able to borrow at the new level.
But Abbey said it would look at individual borrowers' credit scores and ability to repay the loan when deciding how much it would lend.
Standard income multiples have not changed substantially since interest rates were at 15 per cent, and Abbey said it was "sensible" to review income multiples in light of "the current climate [of] low interest rates and higher house prices".
The move comes on the back of research that showed 17.3 million British adults were unable to get on the property ladder, with 7.4 million people citing house prices as one of the main reasons.
Nici Audham Gardiner, Abbey's mortgage product executive, said: "There are people who feel that they do not want to get on the property ladder, but those who do face many barriers, of which the most notable is the cost of homes.
"We have made changes to our Abbey mortgage proposition to help more people, especially first time buyers, purchase the home they want."
However, experts expressed concerns that borrowers would take on more debt than they could afford, particularly given that interest rates are expected to rise.
Melanie Bien, associate director at independent mortgage broker Savills Private Finance, said the "unprecedented" level of borrowing would be "useful in helping people afford the property they want".
But she said it was vital that borrowers did not overstretch themselves.
"If they do, an interest rate rise or two could be catastrophic," she said. The Bank of England is strongly tipped to raise interest rates by 0.25 per cent to 5 per cent next week.