This might be an American TERPS and FAAO 7110.65 (ATC Manual, similar to MATS UK) explanation, but technically when ATC vectors a plane to intercept final, it is replacing the intermediate segment so the plane intercepts final no later than 3 miles outside of the FAF at the intermediate segment altitude or at a position to descend to that altitude at normal descent rates (less than 200 ft/nm).
Long sentence to say ATC can ONLY radar vector a plane to a point outside the FAF, in a position to be configured, intercept the final course ready to start the final. If one is non-radar (procedural ATC), they cannot clear, or vector, one to anywhere EXCEPT to a published IAF for the approach. NO shortcuts authorized.
Be very careful about shortcuts in mountainous terrain!!
GF