Savers are unfairly losing out from the rate cuts, consumer groups say
The returns paid on the most common type of savings are at record lows, the Bank of England has said.
Branch-based instant access and notice accounts, tax-free ISAs and bonds are all offering the lowest rates since records began, the official data shows.
It follows the Bank Rate being slashed from 5% since October last year to 1%.
However, many mortgage customers have benefited after interest charged on both standard variable rate and tracker mortgages for new customers hit a low.
Branch-based notice accounts were paying an average of just 0.29% in January, down from 0.9% in December and 3.9% in January 2008, the Bank of England figures showed.
AVERAGE SAVINGS INTEREST RATES - JANUARY 2009
Instant access accounts: 0.51% (Jan 08: 2.77%)
Notice accounts: 0.29% (Jan 08: 3.7%)
Tax-free ISAs: 1.38% (Jan 08: 5.06%)
Fixed-rate bonds: 2.35% (Jan 08: 5.36%)
Source: Bank of England
Interest rates on branch-based instant access accounts slid to an average of 0.51%, compared with 0.81% in December - and sharply down on the average returns of 2.77% being paid a year earlier.
Meanwhile the average tax-free ISA now offers average interest of just 1.38% - a big fall from the 5.06% rates that new customers were getting 12 months ago and the lowest since cash ISA's were introduced in April 1999.
And fixed-rate bonds, which have traditionally offered higher rates in return for committing money for a set period, have seen average rates fall to 2.35% from 3.06% at the end of December and 6.15% at the recent peak in October 2007.
The data does not cover the period after February's interest rate cut from 1.5% to 1%, which was attacked by consumer groups who argued it penalised savers, while doing little to help most borrowers.
And it is likely to add to concern that low returns will put consumers off saving, which would limit the deposits that banks and building societies have available for mortgage lending.
The figures also highlight the difficulty for people relying on income on their savings to boost their income - especially pensioners.
Adrian Coles, director-general of the Building Societies Association, said the latest rate cut was an "assault on savers".
The Bank of England's figures offered better news for many mortgage holders - about 50% of whom have tracker, discount or variable rate (SVR) mortgages.
The average tracker rate for someone with a 25% deposit fell to 4.5% in January from 4.92% in December.
SVRs were at an average of 4.67% from 5.38% the previous month, and are expected to fall further in February as lenders pass on further base rate cuts.