A: Read the teachers' conditions of service at www.teachernet.gov.uk_doc888020050810%20STPCD%20SECTION%20%202.doc. As well as outlining aspects of the job it states that "a teacher shall perform any directions which may reasonably be given by the headteacher".
Heads of department could be seen as acting on behalf of the head. Teachers are required to be in school for 195 days and work for 1,265 directed hours. The induction regulations protect NQTs from unreasonable demands, such as taking non-teaching roles. This could cover presenting something at a meeting, but you're on dodgy ground. Ordering stock is one of the 24 administrative tasks that teachers haven't been required to do for the past two years. You should be doing all aspects of a teacher's role well and not getting distracted.