[martinald]

Definitely UK. Usual reasons (very very cheap, like $20 and then $20/yr filing fees), good legal system, you can do nearly all tax/regulatory paperwork online/through APIs (in fact, it's nearly impossible to do it by paper now).

Corp tax is 20% and up to £~45k pa you will pay no further income tax on dividends drawn down (though I think this is changing this year to 5%).

Flat rate VAT scheme is helpful for smaller companies.

But by far the best thing is the ridiculously good tax breaks the govt offers for startups, esp tech.

SEIS allows investors tax refunds for 50% of their initial investment, plus 25% if you fail. Which means for every £1 they put in, the govt is 'underwriting/giving you' £3. And if you succeed they will pay no further capital gains tax on their realised gains.

R&D allows you to get back 23% of qualifying R&D costs in cash (or deducted off your corp tax bill).

Put those numbers together and you can see why you should incorporate in the UK...