Tony Blair has renewed his attack on Tory spending "cuts" amid accusations his figures are misleading.
The Conservatives said the poster was misleading
On Thursday Mr Blair conceded a poster stating: "The Tories will cut £35bn from public services", referred to a "cut over Labour's plans" in 2010/11.
But he repeated the claim in a speech to party activists in Wales, saying the Tories would spend £50m less on services in each constituency.
The Tories said Mr Blair's "smear" tactics were a sign of desperation.
At a photocall on Thursday, Mr Blair conceded the Tories were merely planning smaller spending increases than Labour but he insisted their plans would still lead to cuts in services.
During heated exchanges with reporters he said: "They're saying they're going to spend £35bn less - go and ask them how they can spend £35bn less and not end up affecting frontline public services."
He claimed the Tory proposals were the equivalent of sacking every doctor and teacher in the UK.
Shadow Chancellor Oliver Letwin hit back, saying Labour's poster was a "desperate attempt to deflect attention after people saw the flaws in Labour's 'vote now, pay later' Budget."
The Tories stressed not a single doctor, teacher or nurse would be cut under their plans, with savings to come instead from cuts in bureaucracy.
Tory co-chairman Liam Fox said: "We have said we will be spending more, year on year over and above inflation.
"And to call that a cut is at best a misrepresentation, at worst a downright lie."
But the prime minister continued the same theme on Friday, telling the Welsh Labour conference that a Conservative government would have "devastating consequences" for public services.
He said Labour will put opportunity, prosperity and the quality of public services at the core of its manifesto.
"New Labour showed we had faced up to the fundamental changes to the country which happened when we were in opposition," said Mr Blair.
"The programme of cuts the Conservatives now propose show they have not changed at all and do not accept the changes we have made.
"They do not accept the economic stability, the public service investment, the national minimum wage, tax credits for pensioners and hard-working families.
"A Conservative government would put this all at risk."