Mortgage customers should enjoy base rate cuts too, Which? says
Banks should reduce standard variable mortgage rates when base rates are cut, Europe's largest consumer group says.
Which? called for "a quid pro quo" between banks and consumers as a survey showed recent interest rate cuts were passed on by just 25% of lenders.
Moneyfacts found that banks including Northern Rock had not passed on the full 0.5% base rate cut to UK lenders.
The British Bankers' Association told the BBC: "There is scope to reduce rates to customers."
Which's personal finance campaigner Phil Jones told the BBC: "It's becoming clear that we're facing a worsening time in the housing market. As banks are receiving support from the public at large, there has to be a quid pro quo."
He added: "We think in current circumstances, the consumer deserves a break."
The call, to coincide with Which's publication of its banking reform campaign, comes a day after the financial information service Moneyfacts reported that the 0.5% UK base rate cut two weeks ago was not passed on to standard variable rate (SVR) mortgage customers by three-quarters of lenders.
Moneyfacts' mortgage expert Darren Cook said: "Some lenders have announced a reduction in their SVR and have reduced their rate by the full amount. However, a growing number have chosen not to do this and only passed on a proportion of the cut or none at all."
The survey showed that HSBC had not cut its SVR at all, Northern Rock had cut it by 0.15% and Nationwide had cut it by only 0.3%.
The British Bankers' Association sounded an optimistic note when contacted about the call from Which?.
A spokesman told the BBC: "As liquidity returns, because of recent government and central bank actions, banks are again able to lend to each other and at lower rates. Early signs are that BBA Libor rates - the benchmark of real interest rates - are beginning to come down."
She added: "As the rates which banks charge each other reduce, there is scope to reduce the rates to customers."