The 2026/27 tax year is the last one where savers under the age of 65 can use the £20,000 allowance to earn tax-free interest on their savings, and there are some pretty attractive interest rates on the market at the moment. The consumer group Which? has conducted a detailed study of ISA providers and rates to name the very best right now, with an appealing 4.6% rate in first position.

While Stocks & Shares ISAs typically give higher returns, many savers still feel more comfortable storing their money in a Cash ISA as it carries less of a risk. However, from April 2027, the annual allowance for Cash ISAs will drop from £20,000 to £12,000 for people aged under 65. This means that most savers have less than 12 months to earn tax-free interest on up to £20,000 in a Cash ISA. Many savers are now looking for the very best returns to take advantage of the annual limit before it changes.

Which? has examined the current Cash ISAs on offer for Brits at the moment, identifying an attractive 4.6% instant-access account as the best.

The rate is offered with the Plum Cash ISA, which has a minimum investment of just £1. It is opened through Plum's mobile app, and interest is paid monthly.

The rate includes a Plum bonus of 2.07% AER (variable), and it only applies if money is kept for 12 consecutive months and other conditions are met. After 12 months, the rate will be 2.54% AER (variable), and the transfer-in rate is 4.08% AER (variable), which includes a bonus rate of 1.54% AER (variable).

Not only does it have a leading rate, but Plum earned a 73% provider customer score in the Which? research, which earns it a recommendation from Which?.

The account is fully flexible, so it doesn't require savers to lock away their money for a set period of time. Customers only need the Plum mobile app and their National Insurance Number to open the account.

The consumer group listed other Cash ISAs with the highest interest rates on the market in its report. In second place is the Vanquis Bank 1 Year Fixed Rate Cash ISA (4.46%), followed by the Vanquis Bank 2 Year Fixed Rate Cash ISA (4.48%).

The best Cash ISAs to open at the moment, according to Which?, are:

The above rates were sourced from Moneyfacts on 7 April 2026.

However, Plum didn't rank as the number one ISA provider in the group's research. That title goes to Charter Savings Bank with a provider customer score of 82%.

That is followed by Bank of Ireland UK with a score of 81%, AA with a score of 78% and Starling Bank with a score of 78%.

"We've asked thousands of savers to rate their bank or building society, enabling us to create unique customer scores for all the major providers," Which? says in its report.

"We've also analysed thousands of savings products and given each provider an overall interest rate score, highlighting which companies offer consistently competitive rates."