Two more mortgage lenders have failed to pass on last week’s interest rate cut in full to some of their borrowers.

Nationwide Building Society is reducing its base mortgage rate by just 0.3%, while Abbey is cutting its equivalent by only 0.15%, despite the Bank of England base rate falling by 0.5%.

Abbey also announced that it was reducing tracker rates for new customers borrowing up to 75% of their home’s value by just 0.1%, effectively increasing the differential above base rate by 0.4%. The groups join only two other lenders who have so far announced they will not pass on the full reduction.

Nationalised bank Northern Rock is cutting its standard variable rate by only 0.15%, while HSBC is not reducing its standard variable rate at all.

The news came as figures showed that the gap between the cost of tracker mortgages and official interest rates has soared five-fold during the past year. Nationwide justified its decision saying its SVR, which it calls the base mortgage rate, would be lowest on the high

street at just 6.19% following the 0.3% reduction.

It is no longer offering its base mortgage rate to new customers through intermediaries, with people now needing to apply to it direct.

It is also not offering the loan to new customers wanting to borrow more than 75% of their home’s value, although existing customers will continue to revert to the base mortgage rate when their current deal expires as usual.

A 0.15% reduction will save customers with a typical £150,000 mortgage £14 a month, while a cut of 0.3% will shave £28 off monthly repayments. But if the groups had passed on the full 0.5% reduction, borrowers would have been £46 better off a month or around £550 a year.

So far, only around a fifth of the 85 lenders with an SVR have announced plans to pass on the recent cut, including mortgage giants such as Halifax, and Lloyds TSB and Cheltenham & Gloucester, as well as smaller players such as the Co-operative Bank which today said it would be reducing its SVR by the full 0.5%.