The cost of a limited company is £12. It’s formed in a day. Use https://www.ukpostbox.com if you need an address.
The legal system is well known and entrepreneur friendly. Accountancy and company admin are simple and relaxed. HMRC is supportive. You can pay dividends on a flexible schedule.
There’s a very large ecosystem of financial support, innovation grants, incubators, accelerators, angel networks and VC firms.
Flip to the US for later stage funding. Nice problem to have.
Needless to say, IANAL, this is not financial advice, crayons, etc.