Your event may be supported by professionals working as artists, providing entertainment, stewarding, security, childcare or working with young people.
Remember to be clear on what basis professional staff are employed. Unless you are an established organisation it is unlikely you will be employing them on a PAYE basis. It may be that for example a school providing the venue for your event, needs to employ a caretaker to prepare and make good the site. Your relationship with this person is likely to be important for the success of the event and its future.
It is more likely that you will be employing people on a casual or freelance basis. Advice about contracts can be found in the Legal Stuff section of this website.
As well as a signed agreement make sure before you pay someone that they provide you with an invoice that shows a personal address, the date and their unique tax reference number.
Make sure that as many staff as possible are present at a briefing before the event and explain what it is about, highlight customer service and safety including supporting access needs of disabled people, evaluation forms etc.