30% Non-resident alien tax on BMI statement

[CFJ]

I'm a Taxi member living over the pond in the UK. In my recent BMI statement i've been taxed 30% by IRS at source as a 'non-resident alien'. I wondered if some of the more experienced international Taxi members could help me out in how to fix this. I think the UK has a treaty in place but i'm not so sure on what to do first. Any advice will be hugely appreciated!!