VFRPILOTPB -
I have just picked up my well-thumbed copy of CAP413 (CAA r/t manual). I refer you to p58, "Examples of Air-Ground operators phraseology" This clearly states, and I quote
"A/G operators should not use the expression "at your discretion" as this is associated with the service provided by FISOs".
Even then, a FISO even, is not able to issue instructions or advice of his own volition. They are permitted to pass instructions to vehicles, personnel, aircraft etc on the manoeuvring area. At all times in the air communications with pilots will only be the passing of information. CAP413 p36....
Remember, the operators of an A/G facility need to have NO FORMAL ATC QUALIFICATIONS - or even flying qualifications. You could be talking to the Tea Boy, or the office clerk.
To summarise,
A/G - (Callsign XXX Radio)CAN ONLY give information
FIS - (callsign XXX Information) Operator is a CAA approved Flight Information Service Officer. It is NOT a control service, but an information service. Info will be relevant to safe and efficient conduct of flight
ATC - (Ie., Radar, Approach etc) Fully qualified ATCOs and they do issue instructions.
Hope that helps. I suggest that you carry on with what you are doing, and if it happens again, a quiet word in the airfield management's ear, and if that doesnt work, there is always the chaps at CAA SRG in Gatwick!
Tailwinds