Only 33 of the top 100 easy access cash ISAs are classed as "clean", Spring has stated, as they come with no short-term bonus rates, withdrawal limits or other restrictions.

In research conducted by Moneycomms, Spring revealed that just three of the top 10 easy access cash ISAs offer no bonuses or restrictions, meaning that savers looking to make the most of their tax-free savings should look beyond the headline rate when choosing an account.

Across the top 100 easy access cash ISAs, the savings app found that 47% of easy access cash ISAs restrict the number of withdrawals a saver can make, while 16% include a short-term bonus rate. The average bonus rate sits at 1.64%, with bonuses lasting for 12 months on average.

These bonus rates are particularly prevalent towards the top of the market, with eight of the top 20 accounts including a short-term bonus.

Furthermore, 9% have another account restriction, such as requiring savers to hold a current account with the provider to qualify.

Across the top 100 easy access cash ISA accounts, the average interest rate stood at 3.69%.

Head of money at Spring, Derek Sprawling, stated: "Cash ISAs provide savers with a tax-efficient home for their money and, for those choosing an easy access account, being able to access their savings when they need them is likely to be an important part of that decision.

"However, our analysis shows that savers need to look beyond the headline rate. Almost half of the top 100 easy access cash ISAs restrict how often customers can withdraw their money, while others rely on temporary bonuses or require customers to meet additional conditions.”

"A competitive headline rate can be attractive, but savers should understand what sits behind it. That means checking whether the rate includes a bonus that will expire, how often they can access their money and whether they need to hold another product with the provider to qualify. With only a third of the top 100 accounts offering a clean proposition, shopping around and checking the terms can help savers find an account that provides both a competitive return and the flexibility they expect from easy access savings."

Personal finance expert at Moneycomms, Andrew Hagger, added: "The easy access cash ISA market mirrors the age-old situation we see with traditional savings products, with many accounts not truly ‘clean’ easy access accounts.

"ISA customers should be careful not to plump for an account just because it’s near the top of the best buy tables – if they look more closely, they may find that the rate is boosted by a temporary bonus or there are restrictions on the number of withdrawals they can make – so not truly easy access as providers and comparison sites would have you believe."

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