A contractor is classed as an individual who starts working for a company at one set date with the intention of ending on another date. A contractor can only be classed as a contractor if the company that is hiring them deducts their tax at source. This means before they pay you they will hold back any tax that is due to HMRC and pay this on your behalf. They will also typically have day rates as opposed to an annual salary or a weekly rate. For the avoidance of any doubt if you pay your own taxes you will be classed as a self-employed individual and not as a contractor.