Item 42 (page 6) of "
Tier 5 (Temporary Worker) of the Points-Based System – Policy Guidance" says, among other things:
To apply under Tier 5 (Temporary Worker), you must have a sponsor. A sponsor is an United Kingdom based organisation that you want to work for (for Government Authorised Exchange the sponsor must be an overarching body) in the United Kingdom.
The words "United Kingdom based organisation" would seem to answer the original question.