Some of Britain’s leading banks and building societies are paying such miserly rates on easy-access Isas that savers would be better off in taxed accounts.

Halifax, part of Lloyds Banking Group, which is 43%-owned by the government, and Nationwide building society are among those guilty of the practice, which in effect cancels out consumers’ tax breaks.

Savers have piled into cash Isas in recent months to beat ultra-low interest rates, as Bank rate has remained at 0.5% for 10 consecutive months. You can shelter up to £3,600 in a cash Isa and interest is tax-free. The allowance will rise to £5,100 for the under-fifties from April 6, having already gone up for the over-fifties last year.

However, research conducted by Moneyfacts, the data provider, for The Sunday Times found that Nationwide’s Instant Access Isa pays only 0.25% interest on a £3,600 balance, while its average easyaccess savings account pays 0.5%. After tax, a basic-rate taxpayer would earn 0.4%, while a higher-rate taxpayer would earn 0.3% — more than with the Isa in both cases.

Halifax’s average easy-access Isa pays 0.3% interest but its average easy-access savings account pays 0.49%. This is worth 0.39% for a basic-rate taxpayer and 0.29% for a higher-rate taxpayer — only a fraction less than the Isa rate.

Michelle Slade at Moneyfacts said: “They are not offering savers any incentive to use the tax wrapper. Most people automatically expect Isa rates to come out better than plain savings accounts. It is surprising to find they may not.” Moneyfacts also found that for the first time since their launch in 1999, the top variable Isa pays less than the best standard savings account.

Standard Life offers the best no-notice Isa at 2.65%, whereas Coventry building society pays 3.30% on its standard easy-access account. This is worth 2.64% after basic-rate tax and 1.98% to a higher-rate taxpayer, so you are still better off with the Isa — but the figures demonstrate how cash-strapped banks and building societies are abandoning Isas in favour of standard accounts where there are fewer restrictions on the amount you can deposit.

Meanwhile, Cheltenham & Gloucester pays only 0.05% on its cash Isa — just 50p on a £1,000 balance in a whole year, or 10 times lower than Bank rate. Alliance & Leicester and Santander pay 2% interest on their online Super Direct Isas but only 0.1% on an Isa taken out at a branch.

Andy Hutchinson at Nationwide said: “There can sometimes be a difference in interest rates between our Isas and normal savings accounts, as they are managed independently of each other. For both types of accounts, we consider the rest of the market before setting a particular rate.”

Hutchinson pointed to Nationwide’s two-year fixed-rate Isa paying 3.5% a year and said its easy-access Isa pays 0.5% interest on balances above £25,000.

Halifax said: “We offer a competitive range of savings accounts on the high street. Customers have told us they are looking for longer-term stability for their savings, so our Isa focus has been on the longer-term fixed market.”

Here we look at your options. All deals mentioned accept transfers in from other Isa accounts.

FIXED-RATE ISAS

Many people will be reluctant to tie up their money when a rise in Bank rate this year is likely. However, state-backed Northern Rock has launched a “stepped” cash Isa that raises the interest it pays each year you are tied in. Its three-year stepped Isa pays 3% in year one, 4% in year two and 4.5% in year three, which gives an overall rate of 4%. This is equal to the best three-year fixed-rate Isa, which is from Marks & Spencer Money.

Other attractive rates on fixed-rate Isas include Skipton building society’s 3.2% one-year fixed-rate Isa. Santander pays 3.5% a year on a two-year fixed-rate Isa.

VARIABLE-RATE ISAS

If you need access to your money, better deals could soon be available. “I think we will see an even bigger rush of new rates coming out towards the end of the tax year,” said Slade. “We could see rates going up a lot more before this season is over.”

The best variable rate is 3.01% from Manchester building society, including a 1 percentage point bonus for the first 12 months, but you must give 60 days’ notice to access your money. The best no-notice cash Isa is Standard Life’s Direct Access, which pays 2.65%.

ISA TRANSFERS

Many Isa deals contain introductory bonus rates, meaning the rate you receive goes down after a set time — usually between six months and a year. “Take advantage of introductory bonuses but remember to transfer your Isa when the bonus ends,” said David Black at Defaqto, the data firm.

If you want to transfer an Isa opened in the current tax year, you have to transfer the whole amount. Older Isas may be split between providers. You can switch cash Isas to equity Isas but not the other way round. Not all savings institutions accept transfers in from other Isas.

Black warned savers to make sure they follow the transfer procedure correctly, or they will risk losing their Isa allowance. Do not cash in your old Isa before opening the new one.