HM Customs & Revenue issue guidance to employers and you can read the details here,
http://www.hmrc.gov.uk/employers/employee_sick .htm#7 and click on "Evidence of incapacity for work"
It says medical evidence should be accepted unless there is compelling evidence to the contrary. He can ask HMRC for a formal decision once his employers have given their reasons in writting.
fiesata employees need only to have done some work to have possible entitlement to SSP, they need not have worked for eight weeks.