You keep going on about the 90/180 day rule applying in the UK. I have not found anything on-line about this. Could you provide me with a link to the relevant HMG immigration site where this is covered? All I can find is the 6 month duration for visa and visa-exempt entry.
With regard to tax residence, I believe you have to be in the UK for more than 182 days per tax year to be taxed on worldwide income. Being non-resident for tax purposes only exempts you from income tax on foreign earnings, UK earnings are taxed normally. This issue is normally dealt with once a year, i.e. when you submit your tax return.
I used to use the similar rules applicable in the 1990’s and tracked my movements via a spreadsheet to avoid falling foul of the rules by being in the UK to often or for too long. I had to submit a list of my trips a couple of times to HMRC when they asked for proof that I had complied with the rules. I found my initial submission led me to fall foul of the rules, and had to pay extra tax, since I had not counted the days correctly, but once this was corrected I had no further problems with further submissions. I always made sure I had sufficient margin to take care of unexpected delays etc.
With respect to stamping of passports, I think that this is slightly superfluous, since I believe that the details are logged electronically at the UK port of entry passport checks. Thailand stamps passports on entry and exit, however it also appears that the details are logged electronically. My partner, who has dual Swiss/Thai nationality, recently had to renew her Thai passport. She has used her Swiss passport for our trips to Thailand so has never actually presented her Thai passport at Thai immigration. The Embassy staff here in London who processed her renewal application could see that she had not used it on their computer system, and advised her in future to always use her Thai passport to enter Thailand.
In addition we have gone through the extremely simple system of the UK’s EU Settlement Scheme to obtain her settled status here. This does not involve any stamps or entries in her passport, so the only way for the immigration controls to know she has settled status is through their electronic system which is accessed automatically at the relevant passport checks on exit and re-entry. She is allowed to stay outside of the UK for up to four years (continuous absence) before losing her settled status.
The rights of UK citizens in EU/EEA countries is up to the country concerned, not the UK. If the EU/EEA countries continue to be, or turn, vindictive against the UK, there is virtually nothing that the UK government can do. This would result in EU/EEA citizens having more rights than UK citizens. Should the EU/EEA not implement the same form of visa-exempt travelling for tourists from the UK, then I suspect that they will find that UK tourists will find better places to travel to.