The Bank of England's (BoE) first rate cut since 2009 looks unlikely to be passed in full to borrowers, despite the BoE being ready to lend banks as much as 100 billion pounds ($130 billion) to ensure it happens.
The launch of the Term Funding Scheme (TFS) - the BoE's biggest intervention in Britain's banking market in four years - is likely to offer a modest boost to growth. But it also highlights the difficulty of implementing cuts in interest rates as they approach zero.
Governor Mark Carney said lenders had "no excuse" not to pass on August's quarter-point cut in interest rates to 0.25 percent, as the TFS would neutralise the negative impact of the rate cut on bank profits by providing lenders with cheap loans.
But less than a week later, things already look more complicated for the project that is part of the central bank's response to Britain's vote to quit the European Union.
Britain's biggest mortgage lender, Lloyds Banking Group, is holding off cutting its main rate, while First Direct, part of HSBC, reduced the interest rate it pays out on one of its savings accounts by 0.4 percentage points.
"The narrative presented was a bit simplistic," said Ian Gordon, a banking analyst at Investec.
The key point is that British lenders vary greatly in how much they can benefit from the TFS, depending on whether they already have access to finance that costs them less than the 0.25 percent minimum charge for funding from the BoE scheme.
Major lenders such as Royal Bank of Scotland, Barclays and HSBC already have more cash than they have been able to lend out, often from business and personal current accounts on which the banks pay little or no interest.
For them, the TFS will do nothing to reduce the squeeze on their net interest margin - the difference between savings and lending rates that is the main source of profit from lending.
As a result, interest rates on new two-year fixed-rate mortgages - Britain's most popular type of home finance - were likely to drop by less than 25 basis points, Gordon said, as banks' sought to preserve profits and priced in a higher risk of default as the economic outlook darkened.
Existing mortgage rates that tracked Bank Rate would fall, but credit card rates and new business lending - which is sensitive to the economic outlook - would prove stickier.
Bankers say Lloyds and smaller challenger banks such as Virgin Money, Shawbrook and Aldermore gain more from the scheme, as they rely on costlier wholesale finance and savings accounts. Gordon said this gave them scope to cut the interest they paid savers by more than a quarter percentage point - an effect of the TFS which the BoE has not chosen to stress.