Santander - which now owns Abbey - is being accused of slashing the rates paid on its cash ISAs without telling customers.
Accounts which paid an average of more than 4% for seven years were cut without warning to just 0.1% last year.
And the first customers knew of it was a statement sent out at the end of the year.
Santander has told Money Box it was "committed to being one of the most consistently competitive ISA providers." But it refused to provide anyone to come on the programme to answer questions.
Phil Jones from Which? joins Paul Lewis to discuss the issue.
Tory tax break for married couples
The Conservatives are proposing to give four million married couples and civil partners an annual £150 tax break.
It would apply to basic rate taxpayers earning under £44,000 where one partner does not use their full personal tax-free income allowance.
The £550m a year cost would be funded by a levy on banks.
Labour said other families would lose out; the Liberal Democrats called the plan "patronising".
Paul Lewis discusses the proposals with John Whiting of the Chartered Institute of Taxation.
Money Box listeners have contacted the programme with their ideas for how the government should cut the deficit.
This is in response to last week's programme, in which we explored the massive government overspend, which everyone agrees needs to be reduced.
So do Money Box listeners have the answer for the politicians?
Nationwide Building Society plans to stop customers with cash cards withdrawing amounts less than £100 from its branch counters.
It wants people to use cash machines instead, to cut down on queues.
Paul Lewis interviews Nationwide's divisional director of its branch network, Graeme Hughes.
Is there another pension mis-selling scandal brewing?
Over the past four years, about half-a-million people normally in their 50s or 60s have been encouraged to move their pension plan from one provider to another, or to combine several pensions into one.
It is known as 'pension switching'.
This week the Financial Services Authority said that £150m will be paid out in redress for mis-selling, and warned that hundreds of firms are still giving unsuitable advice.
BBC Radio 4's Money Box was broadcast on Saturday at 1204 BST and repeated on Sunday at 2102 BST.