Labour have found an unlikely ally in the shape of Ukip after more than 100 business leaders signed a letter attacking the party's economic plans.

The document was published on the front-page of the Daily Telegraph and showed 103 British business leaders supported a Conservative-led government.

The signatories, including Dragon's Den star Duncan Bannatyne, Apprentice judger Baroness Karren Brady and JCB boss Lord Bamford, showed their support for the government's move to lower corporation tax by 1% to 20%.

The move comes after shadow chancellor Ed Balls revealed that a Labour government would reverse the tax cut in order to slash business rates for small firms.

Patrick O'Flynn, Ukip's economic spokesperson, defended Labour over the intervention and said he was not surprised by the letter.

"I don't think it's a surprise the FTSE 100 executive class are quite happy with the status quo," he said.

"If you look at their remuneration packages and how they've been going up over the last five years – Britain is pretty cushty [in a good situation] for them."

The MEP for the East of England also stressed that Ukip would help small firms over "the corporatist status quo".

But Tory Chancellor George Osborne said the backing from the top business bosses was "unprecedented".

"An intervention on this scale and with this clarity from Britain's business leaders is unprecedented in any recent general election," he said.

"Over 100 business leaders, heading up some of our largest companies and most famous brands, and employing over half a million people, have spoken out.

"And 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."

Chuka Umunna, Labour's shadow business secretary, hit back and claimed no one would be surprised about the letter.

"That's nothing new and under Labour, Britain will have the most competitive corporation tax rate in the G7," Umunna said.

"But whilst the recovery may have reached some firms it hasn't reached many others which is why we will prioritise tax cuts for the smallest firms with an immediate cut in business rates for 1.5 million small business premises.‎

‎"And because we understand that Britain only succeeds when working people succeed ‎we are today announcing our plans to ban exploitative zero hour contracts.

"We don't believe, as David Cameron does, in more tax cuts for the richest in society – the priority is tax cuts for small firms, working people and saving our NHS."

The letter comes with 36 days to go before the general election on 7 May, with Labour one-point ahead of the Tories (36% vs 35%) in the latest YouGov poll.

The Telegraph letter

Dear Sirs,

We run some of the leading businesses in the UK. We believe this Conservative-led Government has been good for business and has pursued policies which have supported investment and job creation.

David Cameron and George Osborne's flagship policy of progressively lowering Corporation Tax to 20% has been very important in showing the UK is open for business. It has been a key part of their economic plan.

The result is that Britain grew faster than any other major economy last year and businesses like ours have created over 1.85m new jobs.

We believe a change in course will threaten jobs and deter investment. This would send a negative message about Britain and put the recovery at risk.