Savers have been warned to closely watch fixed-rate cash ISA "best buys" as rates can change quickly, Investec Save has stated.

Analysis comparing a one-month snapshot of best buys in the one-year fixed rate cash ISA market shows that half of the top 10 changed in the month as rates were cut, with four of the top 20 and nine of the top 50 also dropping out.

Investec Save’s one-year fixed rate cash ISA, which pays 4.20%, remains in the top 10 over the period, but five of the top 10 dropped out, which could affect savers who rely on older best buy lists when making their decision.

A similar level of change was seen in instant access cash ISAs, with four in the top 10 changing in a month, along with eight of the top 20 and five of the top 50 moving.

Average rates for one-year fixed cash ISAs currently stand at 3.79%, while instant access cash ISAs start from 2.63%.

The firm said that once accounts drop out the top 10 or 20 average rates fall, the bottom half of the one-year fixed rate cash ISA pays an average 3.59%, while the bottom half of the instant cash ISA market pays an average 1.67%.

Head of deposits at Investec, David Hunt, stated: "Best buy tables can change quickly, particularly as providers adjust rates in the runup to the end of the tax year. For savers, that means it’s worth rechecking the rate and key terms on the day they apply, rather than relying on an older comparison. This is especially important with fixed rate cash ISAs, where money is typically locked away for a set period and access can be restricted."

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