If there is an element of works that the Main Contractor and Subcontractor disagree on responsibility ie subcontractor says he hasn’t included and isn’t responsible under his interpretation of the documents and the Main Contractor thinks the subcontractor is, does the subcontractor have an obligation to carry out the works? Or can he refuse?
I’m thinking that issuing an instruction to the subcontractor would be the course of action, noting that it does not change the Works Information.
It looks like you have answered your own question.
The Contractor gives an instruction under clause 17.1, which the Subcontractor is obliged to obey, in accordance with the obligation under clause 27.3.
If the Subcontractor still believes this is outside the Scope then the matter should be referred as a dispute, although probably better to sit down together firstly and for the Subcontractor to explain why they believe the work is not included in the Scope.
Yes you should instruct the Subcontractor to carry out the works even if you believe that it is already in their Scope, and under 27.3 they would be obliged to follow it unless it is illegal, impossible or outside their competencies. If the Subcontractor does not believe it to be part of their Works Information (or Scope under NEC4) then they can notify that they believe it to be a compensation event, presumably under 60.1(1). If the Contractor believes it is not one, they would respond stating why not. The only official remedy at that point would be senior representatives under NEC4 or adjudication under NEC3 if they clearly believe it to be one.