Exile.. points noted. As I mentioned earlier, the "non-standard" R/T instructions are a result of controllers finding out from experience which ones produce the required result - ie which ones the crews immediately understand. As for the technical explanation - much appreciated but even that doesn't explain the following typical scenario: Bovingdon hold - roughly southeasterly inbound track with a right turn outbound... As an aircraft starts it's right turn I say "xxx turn right heading 130 degrees" (perfectly standard and non-ambiguous phraseology). The aircraft now turns on to a northerly heading to take it north of BNN... then turns right to the VOR to pick up a heading of 130.. (Happened to me the other afternoon). In miy mind the crew believed that my instructions intended them to start the heading from the VOR.
When started this thread I was expecting someone to say "yes, we're trained always to fly to the beacon before taking up the heading"... but nobody has. Incidentally, in my experience it is only British pilots who do this. Americans, Europeans, South Africans, etc, all simply turn on to the heading. Maybe my colleagues will comment otherwise...?