Alan Rather than creating work for the sub contractor, perhaps you could ask if they are already signed up to a competence scheme. Which will probably cover many of the questions that you are required to ask.

Have you looked at the CHAS appendix 2A. It even provides guidance notes for the contractor/sole trader. Remember you must make allowance for sole traders who have learning difficulties poor literacy skills or no literacy ability. They do not have to have anything in writing but could describe it verbally. CHAS and SSIP members have many thousands of sole traders and micros registered with their schemes. Ask the question, if they are regsitered complaint with an SSIP member you need do nothing more thab verify their status and validity date. Happy to talk about this