Going by the definitions (monthly salary, supply labour, answer to somebody in company etc etc) most contractors (IT anyway) could just as easily be defined by revenue as employeed rather than self employed going by the definitions but the question then arises how companies can offer 'contracts' instead of fixed periods of employeed work if you know what I mean.
Hi TurningGreen, most contractors are encouraged or required by their client company to operate via a limited company (either their own or an umbrella company). This is to help to try and create a separation between the contractor and the client company in order that they are less likely to be deemed an employee by the Revenue.