FAMILY finances have taken centre stage in the General Election battle, with David Cameron pledging not to increase the three main taxes paid by households.

Meanwhile Ed Miliband accused Conservatives of planning a £3.8 billion raid on tax credits for the lower-paid.

Mr Cameron is promising legislation to guarantee a "tax lock", banning rises in the rates of income tax, VAT or national insurance until May 2020.

But Labour - who have themselves pledged not to raise VAT, national insurance or the main and higher rates of income tax, while returning the top rate from 45p to 50p - dismissed the Prime Minister's promise as a "desperate last-minute gimmick" which voters would not believe.

Mr Miliband said he would publish analysis suggesting the Prime Minister was planning to reduce tax credit rates, costing a family with one child £1,600 when their income goes above £23,000 and those with two children £2,000 if they earn over £29,000.

And he said Labour would guarantee tax credits rise at least in line with inflation every year of the next Parliament.

Conservatives have said they will cut £12 billion from welfare if they win the May 7 election, but have so far identified only around £2 billion of the savings.

A party spokesman did not rule out cuts in tax credits when responding to Mr Miliband's charge.

Meanwhile, Liberal Democrat leader Nick Clegg was being joined on the campaign trail by wife Miriam to launch a £610 million promise of free school meals for all primary school children in England.

And Ukip's Nigel Farage was taking a break from campaigning to go to the European Parliament in Strasbourg, where he was fighting a call for EU nations to help resettle migrants arriving by boat in Italy, which he claimed amounted to a common EU migration and asylum policy.

A YouGov poll for The Sun indicated the election campaign was still too close to call, putting Labour on 35% (up one since yesterday), Tories on 34% (down one), Ukip on 12% (unchanged), Liberal Democrats on 9% (unchanged) and Greens on 4% (down one).

Meanwhile a constituency-by-constituency analysis by psephologist Lewis Baston for Westbourne Communications predicted a dead heat on election night, with Labour and the Conservatives winning 272 seats each - with big names like Labour's Douglas Alexander and Lib Dems' Danny Alexander losing their seats, and Mr Clegg's chances of staying in the Commons declining.

Influential pollster and former Conservative deputy chairman Lord Ashcroft suggested Mr Cameron had been mistaken to focus the Tory campaign tightly on the economy and Mr Miliband's perceived weaknesses, and said he should have moved much earlier to win over former Lib Dem voters after the formation of the coalition Government in 2010.

"The Conservative campaign has been focusing on the economy and effectively `Ed Miliband's a w****r'," Lord Ashcroft told LBC radio's Iain Dale show.

"Has that worked or do the Conservatives start to appear to be a little nasty in some of the attacks on Miliband which do seem a little unseemly?

"I wouldn't have started where he (David Cameron) started. I think the campaign needed to have started in 2010 with the collapse of the Liberal Democrats.

"At that point of time, when the Liberal Democrats collapsed from 22% to around 10%, for every one vote that came to the Conservatives, three came to Labour."

Mr Cameron's tax lock promise comes in a speech in the West Midlands which will once again highlight economic policy, including Conservative pledges to raise to £12,500 the level at which workers start paying income tax, increase the higher rate threshold to £50,000 and take estates worth up to £1 million out of inheritance tax.

Urging voters to trust their "gut instinct" on who they can trust not to hike their taxes, he will say: "It is, in fact, the first law of politics: it's Labour who put up your taxes, and the Conservatives who cut them."

But Mr Miliband will accuse the Prime Minister of making "false promises" during the election campaign, as he pledges that a Labour government would help millions of families by ensuring tax credits do not fall behind rises in prices.

Responding to the Prime Minister's announcement, Labour Treasury spokesman Chris Leslie said: "This is a desperate last-minute gimmick from the Tories which nobody will believe a word of. David Cameron broke his promise not to raise VAT last time and if he gets the chance he'll do the same again."

But a Tory spokesman said: "There's one guaranteed risk to working people's finances - Ed Miliband, propped up by the SNP, crashing the economy and putting up taxes, just like he did last time."

And a Ukip spokesman said they were now "the party of low taxes" with their promise to raise the income tax personal threshold to £13,000 and the 40p rate to £55,000.

Meanwhile, former Lib Dem president Tim Farron described both Ukip and the Scottish National Party as "dangerous" as he reiterated his party's refusal to enter a coalition involving either.

"If you wrap yourself in the Union Jack, like Ukip, or the Saltire, like the SNP, you are dangerous, because the politics of nationalism and identity is dangerous and divisive," Mr Farr on told BBC2's Newsnight.

"We would not want to share power in any kind of formal way with a party that wants to break up the country or destabilise it by taking us out of the EU."

In an indication of the Lib Dems likely strategy if the result of the May 7 poll is inconclusive, Mr Farron said in a hung parliament, "the largest party doesn't have legitimacy to form a government on their own because they haven't won the election. But I think they have won the right to start the negotiations."