I am a UK citizen who has just finished working in the US after <2 years. I have claiming tax treaty benefits using article 20a as I am a J1 research scholar. However, I wasn't present in the UK for the 2020-21 tax season. It seems that I am not defined as a UK tax resident according to the HRMC's definitions. But this is odd, because then I wouldn't be paying taxes anywhere, which would defeat the point of the tax treaty.
Below I have copied out article 20a from the tax treaty:
A professor or teacher who visits one of the Contracting States for a period not exceeding two years for the purpose of teaching or engaging in research at a university, college or other recognised educational institution in that Contracting State and who was immediately before that visit a resident of the other Contracting State, shall be exempted from tax by the first-mentioned Contracting State on any remuneration for such teaching or research for a period not exceeding two years from the date he first visits that State for such purpose.
The exemption provided in this Article may be applied by the Contracting State in which the teaching or research is performed to current payments to such professor or teacher in anticipation or fulfilment of the requirements of paragraph 1 or by way of withholding and refund, but in either case exemption shall be conditional upon fulfilment of the requirements of paragraph 1.
This Article shall apply to income from research only if such research is undertaken by the professor or teacher in the public interest and not primarily for the benefit of some other private person or persons
Note: I'm not certain that this is the best sub, but I have seen similar questions asked here. Please feel free to redirect me somewhere more appropriate.