The letter described David Cameron's Conservatives as "the only party that aims to nurture and encourage business rather than hinder or disrupt it" and welcomed Tory plans to reverse the National Insurance hike and simplify corporation taxes and regulation.

The entrepreneurs said that they no longer felt "welcome" in the UK due to the red tape and taxes imposed by Labour, and warned that Lib Dem plans to increase capital gains tax would be "even worse".

The letter, organised by Omnifone executive director Rob Lewis, was initially published with 55 signatures in The Times on Thursday, but the number of entrepreneurs putting their names to it has since doubled to 110.

Among new signatories were Simon Calver of DVD rental firm Lovefilm.com, Michael Stoddart of private equity company Fleming Family, Bodas lingerie founder Helena Boas, Telecity founder Mike Tobin, Wheb Ventures founder Ben Goldsmith - son of Sir James Goldsmith - and Robbie Williams's manager Tim Clark of ieMusic.

The letter warned that "a Brown/Clegg partnership would be totally disastrous for British business, for British competitiveness and for British jobs" and urged voters to do whatever they could to keep them out of power on Thursday.

"Year after year Labour has created ever more reasons for businesses to leave the UK, or for entrepreneurs to set up their new businesses abroad," warned the signatories, who between them have created tens of thousands of jobs in firms paying hundreds of millions in taxes.

"The ever-increasing tax burden and red tape is destroying the very innovation the UK needs to succeed and build jobs in what is a hugely competitive global economy. The sad reality is that entrepreneurs no longer feel welcome in a country run by Mr Brown."

Meanwhile, Lib Dem proposals to increase capital gains tax were "short-sighted in the extreme" and would make the UK a less attractive place for overseas investment, said the letter.

Mr Lewis said: "Neither Brown nor Clegg seem to realise we live in a global economy, where business has to compete on a global stage. Their policies would severely inhibit entrepreneurship, investment and job creation in the UK. We hope we can raise awareness of the dangers to business and jobs of a Lib-Lab coalition administration, before it is too late."