The capital gains tax rate in the US state of Delaware, where Mr Banbury intends to incorporate his new company if the government continues with tax increases, is 6.6% on annual earnings above $60,000 (£46,000).

According to estimates from the Department of Finance and Customs, a 10 percentage point increase in the higher rate of capital gains tax would cost the Exchequer £2 billion in revenue in 2027-28, as that investors change their behavior.

Mr. Banbury spends part of his time in Palo Alto and Silicon Valley, known for their thriving tech start-up ecosystem, estimated at around $2.3 trillion by consultancy Start-Up Genome. It is also home to a number of talented British entrepreneurs who the government must fight to win back, he believes.

He said: “The financial environment certainly partly explains the prosperity of Silicon Valley. I don’t think the Exchequer realizes who they lost and who they didn’t. There are British entrepreneurs in the US with immense power and phenomenal ideas who should exist in the UK.

“If we lose the UK’s leading entrepreneurs, we cannot measure the consequences in terms of capital gains tax loss – we will measure it in terms of the overall opportunity and profitability of the economy British over the next 10 years. The real loss will never appear in the UK’s tax revenue.

“I understand that Labor needs to balance its books, and Reeves is really running out of options – partly because of his manifesto (in which Labor pledges not to increase income tax, insurance national or VAT).

“But we won’t be able to fix the NHS without getting money from big business. What will happen in 10 or 15 years if the biggest opportunities are shifted to America and we are left with everything they couldn’t care less about?

“(The government has) decided to attack something that will jeopardize the future of the nation. There are new forms of technology that will transform the industry – artificial intelligence (AI) is just one of them – and the US tech world will advance at the UK’s expense.