I agree that ICAO phraseology is not always perfect, but then neither is UK phraseology (especially when some of the subtleties will not always be obvious to non-native speakers), however, CAP 413 sets out what should be used in the UK. Although controllers will usually be aware of differences between ICAO and UK phraseology and will understand responses from pilots that come out of the ICAO book, the language used by the controller should be that specified in CAP 413.
I'm more interested in the answer to the original question though. ETOPS refers to a LHR leaflet. Can I get a copy of it? Does the same apply at LGW? Or BHX? Or IOM? Or PLH? Surely if it is OK it will be in CAP 413 or some other CAP but I can't find anything about it.