TENS of thousands of Northern Rock borrowers face being trapped in mortgages charging punitive rates of interest following the bank’s nationalisation last week.

About 175,000 borrowers are thought to have been lured into Northern Rock’s controversial 100%-plus loans over the past few years. They are now likely to find it extremely difficult to remortgage after most lenders pulled out of the market last week.

If they stay with Northern Rock, however, they face a huge “payment shock” with repayments likely to go up by as much as £2,000 a year on a typical loan of about £150,000.

The nationalised bank already has one of the highest rates of repossessions of any lender, and the plight of the 100%-plus borrowers could make matters much worse.

While some were cash-strapped first-time buyers, many others thought the ability to borrow up to 125% of the value of their property was simply too good to miss.

Jamie Lyall, who lives in Newark, Notting-hamshire, and works for a leading high-street retailer, borrowed 104% from Northern Rock in July last year. “My wife and I could have put down a deposit, but the Rock deal enabled us to put the money towards an extension,” he said.

“We are now racing to pay off as much of the loan as we can to improve our remortgage options. However, with our second baby on the way this could prove difficult.”

House prices in his area have been flat, so the family are in danger of sliding into negative equity. Unless they pay down their debt, most lenders will baulk at their business.

Ray Boulger of broker John Charcol said: “The government is in effect a negative-equity lender, while borrowers who owe more than the value of their homes are left with few options as their chance of remortgaging onto another 100% plus deal is slim.”

Northern Rock pulled its range of 100%-plus loans for new borrowers last week in response to heavy criticism from MPs. Alliance & Leicester, Coventry, BM Solutions, Bradford & Bingley and Chelten-ham & Gloucester did the same, leaving limited options for those who have borrowed more than the value of their property.

Mortgages for up to 95% are also disappearing fast. Alliance & Leicester, West Bromwich, Britannia and Barnsley building societies have all reduced the maximum they will lend from 95% to 90% of the value of the property.

Brokers said it would not be long before borrowers need a deposit of at least 10% to get a decent rate. Melanie Bien of broker Savills, said: “Aspiring homeowners as well as remortgagers could soon need equity of at least 10% to find affordable deals as the combination of the credit crunch and falling house prices has forced lenders to readdress their attitude to risk.”

Ian Peace, 38, from Huddersfield, West Yorkshire, succumbed to a 115% mortgage with Northern Rock a year ago at a rate of 5.75% fixed for two years. He said: “We were desperate to move and the loan from Northern Rock allowed us to take a lower price on our previous property. I am now extremely worried that I will be stuck with Northern Rock.”

Northern Rock’s 100%-plus range was structured so only 95% of the loan was secured on the property with up to £30,000 as a personal loan – so if the property was worth £100,000, you could borrow £125,000, or 125%.

Peace, who is married and has two children, borrowed 95% of a property worth £144,000 – or £136,800 – plus an additional £28,200. This added up to £165,000, or nearly 115% of the value of the property.

When he comes to remortgage, he may find he is stuck with Northern Rock. However, the best rate available from the bank is 7.58%, giving repayments of £1,228 compared with his current outgoings of £1,038 – an extra £2,280 a year. He could switch just his 95% secured loan to another lender, but Northern Rock would reserve the right to charge him 8 percentage points on top of the standard variable rate (SVR) on the personal-loan element. This is now 7.59%, so he would be paying a punitive 15.59%.

Even if he could switch to the best no-fee two-year fix from Coop at 5.79% and moved his personal loan to Barclaycard over seven years, he would still face a repayment shock.

David Hollingworth of broker L&C said: “Borrowers could potentially switch the unsecured part of the loan to another lender, but this could be fraught with difficulties in the current climate. Northern Rock should offer these captive borrowers a better deal.”