Bazle

As it took minimal effort, I'm not concerned if I did.

Re certification, I just wrote on the passport photocopy: "I certify that this is a true copy of my passport", and then signed it.

Another article with flowery prose - most likely composed by ChatGPT, I suspect.

Yes. I'm in the UK. The forms seem quite US tax orientated. The W-9 and W-8BEN are IRS forms, which are not applicable to me, but the FATCA form I will need to complete. Most of the questions there are US-related, but not all. In particular, it asks for my Thai Tax Identification Number (TIN), a mandatory question if I have taxable income in Thailand. I do have, as I have bank interest. But there is a section in which I have to explain why I don't have a TIN. If I am not a resident of Thailand or the US, it also asks for my non-Thai address and my overseas TIN.

Perhaps I am not understanding your point correctly, but I do not see any discretion. This article (often referred to as the "tie-breaker" article) usually includes the words "for the purposes of this agreement", and it would have helped if they had included them here. So, you can be regarded as a resident of one country for the purposes of the legislation in that country, but can be regarded as a resident of the other country for the purposes of the treaty. And what the treaty says in relation to the taxation of any particular income or gain over-rides what domestic legislation says (unless there is something in the treaty that says otherwise).

Does that mean the days of arrival and departure are both counted?

Have a read of the OECD Commentary re Articles 15 and 18 of its Model Convention and you will conclude otherwise. https://www.oecd.org/berlin/publikationen/43324465.pdf

Firstly, thanks to @Mike Lister for compiling that document (but I wonder if you are regretting it now ). Secondly, although it is being said that we have almost 12 months to properly understand all of this, I don't agree. There might well be tax planning measures which some people might be able to put in place if those people could be certain of the law. Thirdly, the issue of co-mingled funds must surely raise its ugly head at some point. For example, you have a bank account in your home country into which you pay your pension, rental income, dividends, capital gains, etc. and you bring money from that account to Thailand. What is the nature of the funds remitted? For some people, taking account of the second and third points, it might be advisable immediately to freeze any co-mingled account, and have future monies deposited in brand new (overseas) accounts - possibly with an account for each source of income/gain.

The UK pension is not Thai-source, so that quote is not relevant.

Which office was that, please?

Do others think that BM Liquorice is correct, please?

You said that a pension could end up being taxed twice. I pointed out that the Thais are required to give a credit for UK tax, so that wouldn't be the case.

A copy of the actual treaty is available here: https://assets.publishing.service.gov.uk/media/5a80bddc40f0b623026953eb/uk-thailand-dtc180281_-_in_force.pdf Note Article 23(3): " .... United Kingdom tax payable in accordance with this Convention in respect of income from sources within the United Kingdom shall be allowed as a credit against Thai tax payable in respect of that income. The credit shall not, however, exceed that part of the Thai tax, as computed before the credit is given, which is appropriate to such item of income."

Would using an agent increase the number? TIA.

I hope it's OK to hijack this thread with a third question. If you already have a Retirement Extension, how far ahead of its expiry date can you apply for a further extension? TIA.