Dual Citizen British/US and online business taxes
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.
Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
Dual Citizen British/US and online business taxes

### Response:
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.