2 sheds.
May I quote from CAP413?
Document Purpose
1.1.1 The aim of the United Kingdom Radiotelephony Manual (CAP 413) is to provide pilots Air Traffic Services personnel and other ground personnel, both civil and military, with a compendium of clear, concise, standardised phraseology and associated guidance,for radiotelephony (RTF) communication in United Kingdom airspace.
1.2 Document Applicability
1.2.1 All users of RTF in the United Kingdom are expected to comply with the phraseology described in this manual.
Not just for the benefit of non native speakers. More a LANGUAGE for all users of the airspace.