ED Miliband has pitched the General Election battle in terms of a social divide between Labour being on the side of ordinary workers and the Tories supporting the vested interests of big business and individual tycoons.

The Labour leader sought to frame the debate in this way after more than 100 company chiefs came out in favour of the Conservatives' "long-term economic plan" and big business hit out at the Opposition's plan to end the "scourge" of exploitative zero-hours contracts.

The Daily Mirror in a counter-attack was due to publish a letter signed by 100 Labour supporters, including business chiefs, celebrities and ordinary workers.

Campaigning in Yorkshire, Mr Miliband said: "We have seen today there is a big choice in this election. l believe it is when working families succeed that Britain succeeds; the Conservatives believe that by looking after a few big firms and individuals at the top, everyone else will be OK."

More than 100 senior executives from some of Britain's biggest firms signed a letter to the Tory-supporting Daily Telegraph backing the April 1 cut to 20 per cent in Corporation Tax and warning a "change in course" in economic policy would risk jobs and deter investment.

The letter was awkward for Labour because among its signatories were at least five of its previous supporters, including Scot Duncan Bannatyne, star of the Dragon's Den series, and Sir Cameron Mackintosh, the theatrical impresario.

David Cameron, on the stump in Wolverhampton, claimed the letter from so many captains of industry was a "very powerful message", proving the business community supported the Tories' "long-term economic plan" and was fearful of a Labour victory on May 7.

Describing the intervention as "unprecedented", Chancellor George Osborne said: "The warning from Britain's business leaders couldn't be clearer: a change of course will threaten jobs, deter investment, send a negative signal about our country and put the recovery at risk.

"Britain now knows. No more ifs or buts. Vote for Ed Miliband and Ed Balls on May 7 and jobs and investment and economic recovery will be at risk," he added.

But Labour - which would return Corporation Tax to 21 per cent, still the lowest in the G7, to fund a £400 business rate break for 1.5m small businesses - countered by pointing out the signatories represented only a tiny proportion of British business and had, in fact, not mentioned Labour by name in their letter.

The Opposition also released figures, which showed among the signatories were several Tory donors, who together had bankrolled the Conservative Party to the tune of £9m. It pointed out how a number had received honours including peerages.

The GMB trade union reacted angrily, branding the letter a "list of shame" as it included firms linked to zero hours contracts and blacklisters.

Answering questions from workers at a factory in Huddersfield, Mr Miliband set out his promise of legislation in a Labour government's first Queen's Speech to outlaw "exploitative" zero hours contracts by guaranteeing employees the right to a regular contract after 12 weeks of working regular hours with an employer. Some 700,000 Britons are estimated to be on zero hours contracts.

The Labour leader told his audience: "Less than a week ago, you may have heard the Prime Minister say he couldn't live on a zero hours contract. Well, I couldn't live on a zero hours contract either. I've got a simple principle: if it is not good enough for us, it's not good enough for you and it's not good enough for Britain. That's the way I will run our country; one rule for all."

Reaction to Labour's policy launch was mixed.

John Cridland, the CBI Director-General, warned Labour were "playing with the jobs that many firms and many workers value and need" while Christian May of the Institute Of Directors described the proposals as "unnecessary and potentially damaging".

But Frances O'Grady, the TUC General Secretary, said: "We need a fairer system that guarantees zero-hours workers decent rights at work and stops them from being treated like second-class employees."