The highest rate offered on fixed-term five-year cash ISAs is down 10% on last year, from 5% to 4.5%, according to a comparison report released today.
This compares with a substantially-lower top rate of 3.25% in March 2009.
However, the report, released by independent financial research company Defaqto, shows that the highest instant /easy access ISA rate has increased slightly on last year from 3.15% to 3.3%.
This compares with a March 2009 rate on easy access ISAs of 3.61%. Rates on instant access ISAs have demonstrated considerably less range than those of longer fixed-term ISAs.
At 3.61%, Barclays' Golden ISA was the highest instant/easy access product rate over the last four years, while Santander's Direct ISA Issue 9 at 3.3% is the highest rate offered today.
Santander has provided the highest ISA rates for the last three years, at 3.3%, 3.15% and 3.5% for its Direct ISA Issue 9, Flexible ISA Issue 3, and Flexible ISA respectively.
Defaqto's banking specialist David Black said: "We've really entered the peak ISA subscription season and are seeing new launches and selected rates increased on an almost daily basis as providers battle for their share of the market.
"It is well worth shopping around for the best deal, and reviewing your existing cash ISAs, because there are huge differences between the interest rates paid even for Cash ISAs of similar terms. For example, rates on easy access Cash ISAs vary from 0.10% to 3.30%.
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