New UK Author Question W-8 BEN form

Hello there, could someone please advise how I set up as a UK author? I am currently in full-time employment and hope to do as part-time. I’ve had a look at the W-8 BEN form but I’m not sure what to put in section 7 - reference number.

If someone could help it would be much appreciated.

Thank you,

Damien

Tax Information & Form W-8 Requirements for non US Authors:

@kowalski

Under Tax ID Type choose Foreign Tax ID Number, and in the box Tax ID Number this is the UK UTR Number every taxpayer is given. Your Unique Taxpayer Reference number is 10 numbers long. Otherwise enter your National Insurance Number. PLEASE NOTE THIS INFORMATION ONLY APPLIES TO UK RESIDENTS.