If the successful applicant wishes to be treated as self-employed, you must ensure the person concerned is registered with HMRC as self-employed. S/he should be able to show the 'employer' a letter to that effect, and therefore will be responsible for his/her own tax and NI liability.
It is essential that the 'employer' is satisfied of this, since if, on investigation, HMRC decide that the relationship with the 'employer' looks more like one of employment, they can reclaim any outstanding tax and NI liability for the past six years from the ‘employer’. There is more info on the HMRC website, including an Employment Status Indicator Tool.
Download a Contract for Services template from CIPD. This sets out an agreement between an organisation and a contractor.
Please be aware that the information on this page does not consitute legal advice and HR advice should always be sought.