George Osborne, who oversees the tax agency, said a criminal investigation into HSBC was not within his remit.
IFS director Paul Johnson said the promise wasn't realistic.
The three main parties all held events as the campaign proper for the May election kicked off
The divide between Lib Dems and Conservatives is growing rapidly as the general election approaches
There is wide public support for making the likes of Amazon and Facebook pay their tax
George Osborne claimed victory a budget battle with the EU, saying the UK had halfed what Brussels had demanded, but EU officials said payment had merely been delayed
Leaked diplomatic proposals reportedly reveal deadline for final negotiation of controversial bill to Brussels to be postponed until after UK general election
George Osborne described a report of Angela Merkel's warning over the British government's statements on immigration as "a little bit thin"
Britain's government will pay off part of the nation's First World War debt as part of a redemption of bonds stretching as far back as the eighteenth century.
David Cameron said he would refuse to pay the 2.1 billion euro bill by the Dec 1 deadline, as the row highlighted growing Euroscepticism in Britain