Image caption The move will affect about 850,000 borrowers

The UK's biggest mortgage lender, the Halifax, has confirmed it is raising its standard variable mortgage rate (SVR) from 1 May.

The Halifax said the rise - from 3.5% to 3.99% - was due to the higher cost of raising funds for mortgages from both savers and the financial markets.

On Friday, RBS raised the rate on two of its mortgages from 3.75% to 4%.

This affects 200,000 borrowers with RBS and NatWest offset mortgages and home loans from RBS's One Account range.

The changes have been announced at around the time of the third anniversary of the Bank of England cutting its bank rate to a historic low of just 0.5%.

"Halifax has written to customers advising them it is raising the cap or maximum rate it could charge on SVR which usually signals an imminent rate rise," said BBC business correspondent Joe Lynam.

"If Halifax increases SVR from current 3.5% to 4% that could add £16 a month for those with around £70,000 still remaining, or £24 a month for those with £100,000 left.

A move such as this could lead to an increase in problems and arrears Andrew Montlake, Coreco mortgage brokers

"But for those on an interest-only SVR it could mean a sharp 14% hike in monthly payments."

There are many different types of mortgages but experts often use the SVR to compare borrowing costs on home loans.

High funding costs

The Halifax has been part of the Lloyds Banking Group since January 2009, which is now 40%-owned by the government.

It argued that its hand had been forced by market conditions.

"The change acknowledges that the cost of funding a mortgage in today's market remains significantly higher than the longer term average," the Halifax said.

Analysis Last month RBS got a sharp reminder on the inconsistencies attached to being a commercial bank whose majority shareholder is HM Treasury. This month Lloyds, which owns the largest mortgage lender in the land, Halifax, could feel that heat. Raising your standard variable rate to be roughly in line with most other lenders wouldn't ordinarily attract much attention. But if you're the biggest single mortgage provider and 40% controlled by taxpayers, expect a brouhaha. Halifax's two million mortgage customers - most of whom are on fixed or tracker rates which remain untouched - will wonder whether it's fair or warranted to hike up rates at a time when the bank and its parent can and increasingly does borrow money at record cheap rates in both Britain and the Eurozone. They'll also dismiss excuses from Halifax about the extra cost of borrowing which it has to pay other banks on the wholesale markets, and the fact that paying savers higher interest rates to remain competitive has a flip side: borrowers have to pay more.

"The increase to the rate reflects the fact that raising money through retail savings and in the wholesale markets is currently very expensive by historical standards."

Consumer groups have reacted angrily to the news.

"It's shocking, it's coming at a time when people need this thing least of all," said Marc Gander, founder of the Consumer Action Group.

"Banks have never had it so good. They are doing fabulously well and it amazes me that they can't decide to share some of the burden that the rest of us are sharing.

"If they are saying they have to pass on rising costs, why can't they pass some of the good times on as well as the bad times?"

He also said he thought it likely other lenders would follow Halifax's lead.

"They reckon their customers are like sheep and they themselves are like sheep.

"One takes the lead, and I am absolutely confident that the rest will see these guys get away with it so think they may as well follow."

But mortgage specialist Melanie Bien told the BBC she was not hugely surprised by the move.

"Borrowers will be bemused because interest rates are at their lowest that they've been for three years, and there's been no movement there, but the cost of borrowing in the money markets has gone up a bit - this is what Halifax, RBS and other lenders are saying and this is why they now need to put the SRV up," she said.

Ray Boulger, at mortgage brokers John Charcol, said the typical Halifax borrower was likely to have an outstanding loan of more than £100,000 and would thus pay considerably more than the lender had highlighted.

Mortgage interest rates • Variable rates - This means you pay the going rate on your loan. The mortgage rate changes every time interest rates change or, as in most cases, the overall effect of any interest rate changes is calculated once a year and payments are altered accordingly • Fixed rates - The interest rate is fixed for the period agreed - often two to five years. You do not benefit if rates fall, and will face penalties if you try to quit • Capped rates - These are fixed, but if rates fall you pay the lower rate • Cash back deals - This is when lenders offer money back if you take out a particular product • Discounted rates - Under this type of mortgage the borrower is offered a discount off the lender's variable rate. The rate paid will fluctuate in line with changes in the variable rate. The discount applies over a set term Understanding different mortgage types

"If people have an interest-only mortgage their repayments will go up by 14%, regardless of how long their mortgage has to go," he said.

The Halifax pointed out that its new rate was still cheaper than the SVR of many rival lenders such as RBS, Santander, Northern Rock, the Co-Op and the Yorkshire building society.

And it said that many of its SVR borrowers would be able to transfer their loans to cheaper fixed-rate deals, at no extra cost.

"Customers who wish to transfer their SVR balance to a new product with Halifax, or another lender, would not incur an early repayment charge," the lender said.

An RBS spokesman said the rises were down to the higher costs they were incurring borrowing money, which they had absorbed for some time before opting to pass it on to some of their customers.

The news come as families are facing ever-increasing costs of living across the board.

On Friday, record high petrol prices were announced - motoring organisation the AA says the average cost of a litre of fuel is now 137.44p, with diesel at 144.67p a litre.

Andrew Montlake of mortgage brokers Coreco said some Halifax borrowers would still be put under pressure by the increases.

"For many in the current environment, even a small rise in their monthly outgoings hurts in a disproportional manner than it may have done in more normal times," he said.

"There are many who are only able to keep the wolf from the door because rates are low and a move such as this could lead to an increase in problems and arrears."