You said “And as for the ones who want to move, theu can fill their boots - but they would have to give up their British Citizenship if they dont want to pay tax.”.
If they don't want to pay tax being the key context there i.e under an US style system.
A quick Google tells you this is nonsense. The US tax system is much more complicated than that.
I think perhaps you need to do more than a quick Google. US citizens who live abroad have to file a tax return if their income meets the threshold. The low(ish) tax bands in the US, reciprocal tax arrangements and tax credits mean many don't pay anything because the countries they live in have higher tax rate.
Two thirds of US citizens living abroad are below the thresholds and the majority of the rest don't pay anything due to the double taxation safeguards.
A US citizen living in the UK and earning £250,000 would not have to pay any tax because UK marginal tax rates are higher than the US. However a US citizen living in the UAE and earning £250,000 / $312,000 would have to pay around $63,000 to the IRS because the UAE is a zero tax economy.
If we had a system with the same rules as the US, a UK citizen living in the US would end up paying UK tax on anything earned over £125,000.
The US also tax ALL income - not just PAYE - the IRS tax return applies to capital gains, dividends, interest etc as well.
Under what I'm proposing, no-one earning less than £200,000 would be worse off in the UK. Anyone earning more than £200,000 who chose to move abroad to a lower tax economy would still need to pay UK tax on a proportion of their income if they wanted to retain their citizenship.
They could of course choose to do as Boris Johnson did with his US citizenship and give up they're UK citizenship - but it would mean that they had less access UK opportunities.
How would services improve if the tax take falls? Where would the funding for improved services come from? Your reasoning doesn’t make sense. You’d lose VAT from people leaving (wealthier people have more disposable income so tend to spend more on items subject to VAT).
The money comes from borrowing and capital investment which improves services and increases GDP thus reducing the GDP / debt ratio. Its basic Keynsian economics which successfully rebuilt this country post WW2 until the destructive consumer driven nonsense that is Friedman's free-market ('trickle down') economics was promoted in the 80's.
Wealthier people spend a far smaller proportion of their income on consumption. VAT is regressive, it disproportionately impacts lower earners who spend a higher proportion of their incomes on day to day spend and spend more over time due to not having the luxury of being able to fly abroad to go shopping, having to buy cheaper goods which need replacing more often and buy things on credit which ultimately costs more.
Terry Pratchett explained it well through the Sam Vimes theory of socioeconomic unfairness (boots theory)
No one with any basic understanding of simple economics and maths can think that bringing in policies encouraging those that contribute the most to the tax system to leave will improve the economic situation in the UK.
Anyone with a basic understanding of economics would know that the arguement that raising taxes encourages higher earners to leave the country is a myth!
The uber wealthy take a lot more from this country than they give. Look at Michelle Mone with the PPE scandal, Lord Rothmere who makes a fortune off influencing society (imo for the worse) through the Daily Mail, the biggest selling daily paper, yet hives all that money off in his offshore accounts, Lord Ashcroft who was happy to be chairman of the Tories while paying virtually no tax.
Even Sir James Dyson - he is one of the biggest tax payers in the UK (including his business taxes) and that is with using every loophole possible to reduce his tax burden, including shifting production to Singapore which to date has led to the loss of over 1000 jobs in the UK.
The idea that the wealthy will leave if taxes are increased has been disproved time and time again - most recently in the UK when the non-dom loopholes was closed. Everyone warned that would cause an exodus which never happened.
Denmark has a top marginal rate of 55%. Someone earning the equivalent of £150,000 there would pay over £70,000 in tax (compared to £48,000 in this country under current tax rates). Around 8% of the Danish population are millionaires compared with just under 5% of the UK population, again showing that high taxes do not cause wealthy people to leave the country.
We have to stop swallowing that myth