Concerns over Rachel Reeves's Budget tax raid have hundreds of tech entrepreneurs planning to leave the UK.Weeks of speculation about the Chancellor's plans, which are generally expected to involve a slew of spending cutbacks and more taxes, have given rise to warnings of a possible exodus. In a final warning ahead of Wednesday's Budget, the Startup Coalition lobby organization stated that if Ms. Reeves targets entrepreneurs with an increase in capital gains tax, founders' faith in Britain will be further "shaken."The scale of the threat was laid bare in a recent survey of more than 500 company founders, as 72pc said they had “already investigated moving themselves or their business abroad”.

The founders represent businesses employing more than 22,000 people and have combined revenues totalling £2.6bn.Worryingly for the Government, more than 90pc of the founders surveyed also said they would consider starting their next company abroad if Ms Reeves presses ahead with plans to raise capital gains tax beyond 20pc.

The levy is particularly relevant for entrepreneurs as it becomes payable once they sell their businesses or shares.Sir Keir Starmer last week attempted to dismiss fears that entrepreneurs could quit the UK, arguing there was “no reason” for them to do so.

As well as a possible increase in capital gains, there are also fears that tax breaks, such as Business Asset Disposal Relief, could be removed as Ms Reeves claims to plug what she claims is a £22bn black hole in the economy.Early-stage businesses will also face increased costs if the Chancellor chooses to raise National Insurance contributions from employers.

Dom Hallas, executive director of Startup Coalition, said founders were not “naive” about the need to sort out the country’s finances. However, he stressed that “there is a limit and it’s important the Government knows where it is”.

He said most young founders are highly mobile and can shift their companies abroad with ease. “As one founder put it to me, their business is 30 people with laptops, there is no hard tie [to the UK],” he said.

As well as the draw of Silicon Valley, founders are being lured by other European start-up hubs, such as Paris and Berlin. Mr Hallas said there is also an “incredible push from the Middle East with Dubai and the UAE”.Portugal, meanwhile, has proposed offering tax breaks for under-35s in a bid to attract talented younger workers to the country.

Henry Whorwood, director of research at the consultancy Beauhurst, said the survey’s findings should be a “massive wake-up call for a Government that desperately needs economic growth”.

One vocal critic of the Government’s proposed tax raid is Sara Murray, chief executive of Big Technologies, which makes electronic monitoring tags. She said that entrepreneurs were under “attack” by the Treasury.

“Everybody I know is looking at moving overseas and for the first time I’m considering it,” she said. Big, which is valued at £400m, went public on London’s AIM stock exchange in 2021.

However, the Chancellor is now said to be considering scrapping an inheritance tax break on AIM shares, causing uncertainty for hundreds of listed businesses.

Last week, Barney Hussey-Yeo, the founder of $500m fintech business Cleo, told The Telegraph he was making plans to move to America. “I’ll leave the UK and won’t start another business here,” he said.

In recent weeks, more than 1,000 start-up founders have signed a letter to the Chancellor, organised by The Entrepreneurs Network, warning against a rise to capital gains tax.Philip Salter, the group’s founder, said last week that for many entrepreneurs the issue was “even bigger than Brexit”.

Warnings of an exodus have sparked a furious response from leading Labour donor Dale Vince, who said recently that wealthy founders threatening to quit Britain because of higher taxes should “f— off”.

He said: “If people only live here because they pay less tax, they should “f— off. This is a brilliant country. There’s no way people won’t live here because of a fairer tax system.”

A Treasury spokesman said: “The Chancellor has vowed to lead the most pro-growth Treasury in history.

“We have already taken action to deliver more investment in the UK economy by fixing the broken planning system and setting up a new National Wealth Fund, and the International Investment Summit secured a record-breaking £63bn in investment commitments.