Considering the evidence: personal service
The basic issue in relation to substitution or delegation of work is whether or not an engager requires a worker to perform services personally. This is a necessary condition within a contract for that contract to be regarded as a contract of service but it is not of its own a sufficient condition - see the case of Ready Mixed Concrete [ESM7030]. Where the worker has complete freedom over who will do the job it will be inconsistent with a contract of service (although a limited or occasional power of delegation may not be).
In the case of Dragonfly Consultancy Ltd v HMRC - see ESM7290, Henderson J found that Dragonfly was a one-man company, whose raison d’etre was to supply Mr Bessell’s services - therefore it was obvious that the intention of both parties was that it would be Mr Bessell who would provide the services. This provides the principle that, unless there is evidence to the contrary, the arrangement itself demonstrates the requirement for personal service in one person companies.
In the case of Synaptek Ltd v Young, see ESM7260, there was a provision within the agency-service company contract which enabled Synaptek Ltd, with the consent of the Client, to substitute alternative personnel. Mr Justice Hart stated at paragraph 28 of his judgment that the provision did not give Synaptek any right to perform the services by anyone other than Mr Stuchbury. The effect was that unless and until agreed otherwise, the services did have to be performed by him personally.
If you have established that there is a requirement for personal service you should also bear in mind that any such requirement could be present in a contract for services. As such, this requirement is at best a minor pointer to employment, and you should therefore consider whether or not that requirement is reduced in any way. Likewise, if there appears to be an unfettered right of substitution you need to consider whether or not any restrictions are placed upon that right.
Where your opinion that an engagement is outside IR35 is based upon there being no requirement for personal service, you should make it clear that your opinion has been made on that basis.
See also the guidance at ESM0530 onwards