I'm currently working as a freelancer in the UK and registered as self-employed sole trader. One of the things I'd like to do is use the services of another contractor who is a US citizen that lives and works in the US. Essentially he will be an assistant contractor to support with some of the projects I work on.
Is there anything I need to do from the UK/HMRC side, or do I simply pay the US contractor his fees and declare those as expenses on my self assessment? I don't think PAYE is involved as the person I'm paying is a contractor and lives/works in the US, but wasn't too sure.
If it's simply paying the contractor and declaring fees as expenses, what kind of stuff do I need to keep as evidence for expenses? Would it for example be invoices I bill the contractor?