For anyone that may find it useful here is the vat certificate that HMRC pointed me at on their website. I have attached as  a pdf as forum will not allow editable word.doc to be uploaded   If you have contractor that is being sticky about zero rating you just give them this cert (completed with relevant details) and pay them net of vat.   The cert covers their back with HMRC and doing it this way has worked for me in several cases.     blank proforma vat cert .