Lowell Goddard is the third person to head the inquiry after the previous two were forced to quit.
IFS director Paul Johnson said the promise wasn't realistic.
Cameron has said he will boycott the election debates unless the Green party is also included.
Cameron added that he would be "happy for there to be no debates at all".
Campaigners also criticised "patronising" comments from Baroness Butler-Sloss the former head of the inquiry
The three main parties all held events as the campaign proper for the May election kicked off
According to newly released documents, the former PM also considered putting advertising on the BBC
Blair said the election could be a traditional left versus right contest "with the traditional result"
The poll confirms a seismic shift in Scottish politics away from the Westminster parties
The party has doubled its membership this year, and is now close to overtaking the Liberal Democrats
Tony Blair's father-in-law is on typically robust form talking about the making of a prime minister, politics and mortality
The 'Campaigning Against Ukip' document advised against discussing immigration in favour of "issues where we have a clear policy"
According to the Institute for Fiscal Studies, there are now major differences between the two parties spending plans
The chairman of the largest UK food bank provider blames government policy for the rise in hunger
Eyeing renewed devolution, Yorkshire, with a bigger population than Scotland and bigger economy than Wales, wants to be next
There is wide public support for making the likes of Amazon and Facebook pay their tax
The deal amounts to the biggest transfer of powers to Scotland from the United Kingdom since 1999
A thinktank says the public is facing a "candour deficit" as parties keep plans vague
Shadow minister Emily Thornberry was forced to resign after tweeting a controversial picture
The Conservatives and Labour are facing simultaneous challenges from Ukip and Scottish nationalists that could revolutionize a two-party system
Leader of the opposition party Ed Miliband has he will not "shrink from the fight" in a make-or-break speech after poor poll numbers and rumours of leadership plots
Conservatives take 3 point lead as Miliband revealed as one of the most unpopular party leaders of all time in latest Ipsos Mori polls
Labour's Ed Miliband accused Cameron of putting millions of jobs at risk, as both men addressed business leaders in London
The first minister-to-be accused the Conservatives of leaving women worse off, arguing that women bear the brunt of benefit cuts
Ed Miliband is facing fresh pressure after a poll revealed a fall in support from supporters of his own party
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
41% of the British eurosceptic party's supporters said they believed that 'a house could be haunted', while Labour supporters were more likely to believe in vampires