If you have a Certificate of Coverage from your UK employer that should be attached to the mailed tax return.
If you are a US citizen you cannot use IRS Form W-8BEN
Not sure about Form 8833 So will ask one of our other members who has experience with these matters.
@pk Could you give me a hand here, please?
Social Security website for the Totalization Agreement and Certificate of Coverage US/UK - https://www.ssa.gov/pubs/EN-05-10199.pdf
