Millions of homebuyers are facing a 'mortgage timebomb' as lenders put up interest rates even though the base rate remains unchanged.

Experts are warning that lenders could hike their standard variable rate (SVR) at any time. 

Ten banks and building societies have already put up their rates, costing borrowers hundreds of pounds a year. 

This is despite the fact that SVRs are traditionally linked to the Bank of England base rate, which has been 0.5 per cent for 18 months. 

Culprit: Skipton Building Society hiked its SVR from 3.5 to 4.95 in March despite there being no rise in interest rates

The biggest culprit is Skipton Building Society, which hiked its SVR from 3.5 to 4.95 per cent in March. 

House prices could fall another 20 per cent.

The renewed downturn in house prices is unlikely to be short-lived, according to Capital Economics.

Not only is the market still significantly overvalued, but the lack of mortgage credit and the weak economic outlook also point to prices falling through the remainder of this year and 2011.

Ed Stansfield, chief property economist, commented: “The outlook for house prices is one of sustained weakness. We believe that the rebound in house prices lacked any firm foundation. Thus, at the very least, we expect house prices to drop back to their early 2009 lows.

“However, with most measures suggesting that prices are still significantly overvalued, we think that house prices could well fall 20% from here. 

Advice: For help with a Mis Sold Mortgage and Sub Prime Mortgage Compensation please call 0800 043 1683.   

Complaints are up at the financial ombudsman.

Borrowers whose monthly repayments have been set too low are being left with outstanding debts when they think they've paid off their balance.

A rising number of people in such cases are complaining to the ombudsman regarding how these situations are dealt with.

It needs to be the lenders' fault if the debt is to be written off, says the service.

Known as 'underfunding', these cases can result for a number of reasons - lenders' miscalculations in the length of the mortgage term or quoting interest-only payments in error, for example.

But it will be taken into account whether householders should have known that they were not paying enough.

The case of Clydesdale and Yorkshire Bank.

Homeowners have been hit with hefty bills by Clydesdale and Yorkshire Bank after the lenders miscalculated their mortgage payments.

But on the basis that the blunder was caused by the bank, This is Money is advising people to complain about the call for extra payments. Last week, This is Money's Simon Lambert was featured on BBC's The One Show giving advice to those who have been hit by shortfalls.