Critics have attacked banks and building societies for withdrawing a number of top-paying cash Isa accounts from the market in the past few days.

They argue that with the Bank of England holding its base rate steady at 0.5 per cent, there was no reason for financial groups to pull some of their most competitive products.

Among the accounts that have been withdrawn in the past few days is Barclays’ Golden ISA, which had topped the best buy tables since the beginning of April. The account, which had been paying a rate of 3.61%, including a 1% bonus, has been replaced by one offering a much lower return of 2.58%.

Other accounts that have been pulled during the past week include National Counties’ Guaranteed Cash ISA 2009/2010, which was paying a fixed rate of 3.26% and Halifax’s Direct Reward ISA, which paid a fixed rate of 3% for the first 12 months and allowed people to make up to four withdrawals. First Direct has also slashed the rate it offers on its e-ISA from 3.06% to just 1.98% for the first year, after which it drops to a niggardly 0.2%.

It is thought the ISAs have been withdrawn after providers were swamped with applications as savers scoured the market for the best home for their money in the current low interest rate environment.

At the start of the tax year savings groups traditionally offer very good rates in a bid to termpt people to invest the maximum permissible amount - currently £3,600 - in a cash Isa.

Andrew Hagger, of Moneynet.co.uk, a prioce comparison website, said: “We’re only two months into the new tax year, yet some of the more attractive cash ISA accounts have, in the last seven days, either had their rates slashed or been withdrawn completely.

“It’s starting to look as if some providers may have reached their targets for ISA deposits already and are content to offer a poorer deal to those who haveen slow off the mark.”

The latest figures from the Bank of England show that the average cash ISA was paying a return of just 0.42% at the end of April, down from 0.63% in March and a far cry from the average returns of 4.81% that investors were earning in April last year.

ISAs have been hugely popular with the public since they were first launched 10 years ago.

The latest figures show that 18 million people have taken out either a stocks and shares or a cash Isa, collectively saving £290 billion in them.

People can currently save up to £7,200 a year into an ISA, half of which can be paid into a cash ISA. However, the Chancellor announced in the Budget that the annual Isa limit would be increased to £10,200 from October this year for those aged over 50 and from the beginning of the 2010 tax year for everyone else. Within this total, the amount that can be held in a cash ISA is rising to £5,100.