You should keep a close eye on the reaction of your bank or building society to a change in the Bank of England base rate, as this can have a sizeable impact on your finances.

Some banks pass on potential savings, but others use rate changes to squeeze extra profit from customers. Figures compiled for Times Money show that the two worst offenders since the base rate was cut to 5.5 per cent in December are Intelligent Finance and Manchester Building Society. Both were quick to reduce interest rates on savings accounts, but they have, so far, refused to pass on the benefits to borrowers who are on variable-rate mortgages.

A further 31 banks and building societies – including NatWest, Lloyds TSB, Halifax, Abbey and Alliance & Leicester – cut savings rates more than mortgage rates.

The figures from moneysupermarket.com also highlight four angelic building societies – Barnsley, Chesham, Chorley and National Counties. This quartet left savings rates alone, while easing the pressure on borrowers with a full quarter-point cut in standard variable rates.

Only 14 other providers, including HSBC and its internet-only operation, First Direct, managed to protect savers from the full rate cut while still reducing mortgage rates. Nine of these were small building societies.

Kevin Mountford, of moneysupermarket.com, the price comparison website, says: “It is reasonable to assume that changes in the base rate should be passed on equally to savers and borrowers. This is particularly true for consumers who hold their mortgage and savings with the same bank or building society. However, the industry looks increasingly at changes to the base rate as a chance to recalculate margins.”

Consumers with both their savings and a mortgage with one of the 33 “devils” will feel hard done by, particularly if they have an instant-access savings account and a variable-rate mortgage. The wider the difference between the cuts, the more customers are penalised.

Halifax squeezed savings rates by 0.05 percentage points more than mortgage rates. At Bradford & Bingley and Egg, the difference was a tenth of a point, with a full quarter-point cut to savers but only 0.15 points cut from borrowing rates. Mr Mountford adds: “If consumer’s do not believe that they are being treated fairly by their providers, then they should seriously consider moving.”

In theory, banks and building societies should treat savers and borrowers equally, whether raising or lowering rates in response to base-rate changes. In reality, however, while most savings rates remain closely linked to the base rate, mortgage rates have become less so since the credit crunch began to bite last year. With the wholesale cost of money increasing, many banks have seen profit margins fall, making them reluctant to cut standard variable rates (SVRs) or lower fixed rates for new customers.

Tracker deals for existing customers are unaffected because they are linked directly to the base rate. But many providers, including Nationwide, have increased tracker rates for new customers. David Hollingworth, of London & Country Mortgages, the broker, says: “It is important to be aware that lenders can choose not to pass on a rate cut. But there are lots of deals where borrowers can side-step these issues. A tracker ensures that your deal follows the base rate.”

Saffron Building Society cut its SVR by only 0.19 percentage points, but it is offering a competitive tracker deal pegged at 0.06 points below the base rate for three years, giving a current rate of 5.44 per cent. The deal is for loans of no more than 85 per cent of the property’s value and carries a fee of £699. Intelligent Finance, which has a number of good offset mortgages, is offering an offset three-year tracker at 0.34 points above the base rate, at 5.84 per cent. You can borrow up to 75 per cent of the value of your home, with a fee of £799.

Savers should look at the way a bank or building society responds across the board to a base rate change, says Sue Hannums, of AWD Chase de Vere, the independent financial adviser. “Comparing how a provider treats savers and borrowers can give a clue as to whether it will play fair in the future,” she says. “The most important factor is the interest rate – and if the devils of the banking world are paying better savings rates, go with them.”

Alliance & Leicester cut the majority of its savings rates by 0.23 percentage points last month, but its eSaver account offers the best returns on an instant-access account. It pays 6.5 per cent, with a 0.35 per cent bonus until next January. Bradford & Bingley cut much of its savings range by 0.35 points, but its eSavings account still pays an excellent 6.4 per cent.

Mr Mountford says: “Consumers need to decide which products and deals offer the best value for their situation. The economic climate suggests that we will see more base-rate cuts over the next year, but the willingness of banks to pass these on to customers must be considered when choosing a savings account or loan.”

CASE STUDY

Stuart, left, has an offset tracker mortgage from Intelligent Finance with his wife, Maria Shepherd, on their three-bedroom house in Bromborough, Merseyside. The couple also have £3,000 in a Direct Access savings account with the internet-only bank owned by Halifax.

Mr Southern decided to look for another provider after his savings suffered a quarter-point reduction in interest after the latest base-rate cut. “Over the next month I will be reconsidering all my financial arrangements, including my savings and mortgage deal,” he says. “If I can find the right deal I will switch.”

His mortgage, with £102,000 outstanding, is pegged at 0.64 points above the base rate for two years, giving a current rate of 6.14 per cent. When the deal ends in June the loan will reverts to Intelligent Finance’s standard variable rate of 7.14 per cent.

The 30-year-old says: “My tracker mortgage was cut after the base rate, but it took almost a month to kick in, and my savings fell by the full quarter of a point, too.”