I am a dual British/US citizen living in the EU. I file taxes in the US with my husband. I want to open an account with an online gallery to sell my artwork and as we intend to retire to UK I will base my business out of the UK. Do I have to submit my US tax ID to the online gallery or can I be registered as a British artist? Is it mandatory to use a US tax ID if you have one?
I see no reason why a US ID would be mandatory anywhere in the UK. I'm sure they have their own tax IDs in the UK.
However, if the gallery requires US persons to submit US W-9 - then yes, you're covered under that requirement.