Labour has attacked the Tory pledge to reverse part of the Government's planned National Insurance increase.

Addressing the party's first press conference of the election campaign, Chancellor Alistair Darling said it was "not credible" for the Conservatives to claim they could save an additional £12 billion this year on top of the £15 billion the Government is already cutting.

Prime Minister Gordon Brown said the Tories were basing their entire economic strategy on a "flimsy" four-page press release setting out their savings plan.

He said: "What the people of this country need to ask themselves is this: do the British people really want to gamble your economic future on the basis of a back-of-envelope set of calculations like this?"

Mr Brown said Britain's economic recovery is underway but added: "We are not out of the woods and that's why it's so important to make the right decisions now.

"Get the big decisions wrong now and we'll be paying the price for years to come."