Jan - thanks for the reply - your thoughts were originally my own. However, FISO's in the UK
can issue instructions to aircraft on the ground. That is what my original question relates to - and the R/T phraseology they use.
CAP 410 (UK CAA) Part B refers:
The Flight Information Service Officer (FISO) provides an information service to
aircraft that are flying or about to fly within the aerodrome traffic zone. Under Rule 35
of the Rules of the Air, FISOs at aerodromes are permitted to issue instructions to: a)
departing aircraft about to move or moving on the apron and
manoeuvring area up to
the holding point of the runway to be used for departure; b) arriving aircraft moving
on the manoeuvring area and apron, following the completion of the landing roll; and
c) all other taxying aircraft intending to move or moving on the apron and manoeuvring
area, including the crossing of runways. Elsewhere on the ground and at all times in
the air, information shall be passed.
Now, this suggest that
beyond the holding point you are within your right to do whatever you consider safe and expeditious. However, this is not always the case since FISO's here seem to still maintain a degree of "advisory control" into the runway environment; e.g they can instruct you to "hold short" (instruction) or "take off at your discretion". While the last phrase is NOT a clearance, it surely has to be an instruction, just as "hold short" is. Try entering the runway env. and taking off without the "take off at your discretion.." response from the FISO and you risk getting some stern feedback about your actions
The whole thing seems rather grey to me.