LABOUR has sought to regain the political initiative, after David Cameron unexpectedly ruled out a future Tory government raising VAT, by announcing its own promise not to hike National Insurance.

On a day of high drama at Westminster when the General Election campaign began to move into a higher gear, Ed Miliband sought to put the Prime Minister on the spot, demanding he give "a straight answer to a straight question" by challenging him to rule out the prospect of a future Conservative government increasing VAT.

To Labour's great surprise, the Tory leader turned round and said he would do just that, telling the Leader of the Opposition: "And the answer's Yes."

As Conservative backbenchers roared their support, Mr Miliband remained dissatisfied, saying: "Nobody is going to believe him because of his extreme spending plans."

But then Mr Cameron sought to put the Labour leader on the spot, urging him also to give a straight answer to a straight question and rule out a future Miliband government raising National Insurance Contributions.

However, the Labour leader did not; saying only: "He'll have plenty of time to ask questions after May 7."

Later, Chuka Umunna, the Shadow Business Secretary, said there were "no plans" for Labour to raise NICs if it got into power but later still Ed Balls intervened, saying there would indeed be a promise in the party's manifesto not to raise what has been dubbed the "jobs tax" if Labour won power.

Speaking to reporters at Westminster after PMQs, the Shadow Chancellor said: "We will make it clear in the manifesto Labour will not be raising National Insurance. That will be a clear pledge from us."

Interestingly, the tit-for-tat declarations will deprive an incoming administration of either colour of significant sources of revenue as they seek to balance the books following the election.

But they also close down major vulnerabilities in the campaign. Labour had only this week launched a poster warning voters of the VAT increase, which would hit them if Tories won, while the Conservatives have been warning of Labour's "tax bombshell" on NICs to help it cut the deficit.

The tax declarations come as the election campaign is set to intensify with Westminster rising and the first of three TV events taking place today at 9pm, hosted by Sky and Channel Four.

Political inquisitor Jeremy Paxman will cross-examine Mr Cameron for around 20 minutes before a studio audience asks the Tory leader questions for another 20 minutes . Then, in a separate session, the same process will be undertaken with Mr Miliband.

This format was agreed after the Tory leader turned down a straight head-to-head with his Labour opponent.

On Friday, Labour is expected to undertake a "soft launch" to its election campaign with an event in London.

On Saturday, Mr Cameron is due to give a keynote speech to the Conservatives' one-day Spring Conference in Manchester while SNP leader Nicola Sturgeon will do the same at her party's own event in Glasgow.