As election campaigning enters its final seven days on Thursday, the Tories are claiming Labour would leave a million families worse off by taxing or means testing child benefit.
" This is not only a Tory tax smear but a spectacular own goal for the Conservative Party "
For Labour, which is now campaigning under the new slogan of "schools and hospitals first", Mr Brown said it was the Tories which would hit the pockets of families needing help.
Meanwhile, the Lib Dems are campaigning for a second consecutive day on their plans to help pensioners.
Two polls published on Thursday continue to suggest that Labour has a strong lead.
The MORI/Times poll puts Labour on 48%, the Conservatives unchanged on 30% and the Lib Dems on 16%.
That means Labour are down 7% on MORI's last Times' poll a week ago but MORI says the questions have changed slightly so direct comparisons cannot be made.
The Gallup/Telegraph poll puts Labour on 47%, the Conservatives on 31% and the Lib Dems on 16%.
Labour has announced plans for a campaign blitz through posters, leaflets and telephone canvassing on its "schools and hospitals" theme.
Prime Minister Tony Blair said its message on vital public services would be his "crusade" for the last week of the campaign - and for a second term in office if he won the election.
The Tories have maintained Labour is planning a "stealth tax" on child benefit.
Chancellor Gordon Brown was challenged by Conservative social security spokesman David Willetts to promise that he will not tax or means test child benefit.
The Tory frontbencher says the Labour manifesto contains "weasel words" which would pave the way for the chancellor to introduce the tax.
At the party's morning press conference, Mr Willetts said Mr Brown privately had made it clear that he believes there is a case "in principle" for higher rate taxpayers paying tax on child benefit.
He claimed Labour needs £1bn to fund its plans for a new system of child support, and taxing the benefit would raise at least half that amount.
"It's the latest black hole in his spending plans, he needs to raise the money and his first instinct is always to tax hard-working families," he said.
But at Labour's election new conference, Gordon Brown said: "This is not only a typical Tory tax smear but a spectacular own goal for the Conservative Party."
Mr Brown said he had already made clear child benefit would not be taxed and would remain universal.
He said Labour had made families more prosperous and claimed Tory policies would hit the pockets of families and parents who needed help.
On Wednesday night Mr Hague stuck to his line that polling day would be the last chance for a fair vote to save the pound as he faced questions from voters on a LWT special programme.
But speaking on Question Time, Mr Blair accused the Tories of trying to make the election decision day on the euro because they had nothing else to say.
The Lib Dems are campaigning on their pledge to help pensioners for a second day running.
They are highlighting plans to eradicate "fuel poverty" by introducing a UK-wide home insulation programme.
Lib Dem leader Charles Kennedy said: "We have spoken for older people, we have been the pensioners' opposition in the last parliament."
The party was given a boost on Thursday by former Tory MP Sir Anthony Meyer, the first challenger to Margaret Thatcher's leadership in the months before her fall from office in 1990.
He urged "One Nation, pro-European Conservatives" to vote Lib Dem in constituencies where Eurosceptic Tories are standing.