Quote from Lon Eagle:
To try and help.
If you work in the UK and are a UK resident then the nationality of the firm you work for is irrelevant, I am sure.
I think the form was a W-8BEN form. Where this has arisen is that when I have contacted a US firm based in the States and traded online via them. To ensure I am free of US taxes I have needed to complete the form saying I am a UK resident. The form is a US govt one - not a Uk one. I have certainly never been told a US tax ID number.
Thanks again. I will do more research into this. I appreciate your help.