Cooperative Bank, Halifax, Clydesdale and Yorkshire Bank have all increased their standard variable rates (SVRs) today.

Consumer group Which? has estimated consumers will face an additional £300 million in mortgage repayments over the next year.

Bank of Ireland has announced an increase in its SVR which will take effect in two stages on 1 June and 1 September. RBS/Natwest increased its variable rates for its offset mortgage customers on 1 March and has also increased variable rates for its One Account customers today.

Which? research show 70% of mortgage-holders are concerned about an increase in interest rates. 14% say they are already struggling with repayments. The greatest impact of these latest rises will be felt by ‘mortgage prisoners’ who are unable to move to another provider.

Three quarters of mortgage-holders told Which? that they would be affected if their repayments increased by £50 a month, with 41% saying they would need to cut back on regular spending, 20% would need to reducing savings and 11% would not have enough for essentials.

An increase of £100 a month would see 20% of mortgage-holders not having enough for daily essentials like food and 11% being unable to pay their mortgage. Consumers also highlighted the emotional impact of increases in mortgage repayments, describing them as “devastating” and “a disaster”.

Peter Vicary-Smith, Which? chief executive, said: “Our advice to anyone struggling with their mortgage repayments is speak to your lender straight away. It is encouraging that a third of people we spoke to had approached their lender but worryingly in one in five cases, they said their lenders offered no help at all. This is just not good enough and we want to see banks do more to help their customers who are struggling.

“These SVR rises are the consequence of the lack of competition in the market and the failure of the government to take action to promote competition. This is why the new financial regulator, the FCA, needs to be a watchdog not a lapdog. It must stand up for consumers and stand up to the banks.”

Which? wants lenders and the FSA to do more to protect consumers against unjustified interest rate rises and ensure that consumers are offered the ability to fix their payments at a reasonable level.

Lenders must not be allowed to take advantage of borrowers who are unable to move lender, Which? said.