It is all very well suggsting that pilots say too much on the air, but the system in the UK requires so much more to be said. The controllers asking you to keep clear haven't made this instruction up themselves: I am sure they have been instructed to say it, because SOMEONE somewhere has decided that as some aircraft do inadvertently enter CA without permission, this might help to stop it.
It has been explained to me that oft said phrase came about as a result of an aircraft doing the following at I think Belfast;
VFR flight calls up and reports it's route as from A to B (a point on the southern control zone boundary) and then to C (a point on the northern control zone boundary) and on to another point. A straight line from B to C taking the flight through the control zone.
The controller said nothing in particular to the flight until it was inside the zone. The result was an argument as to did the flight request clearance for the route and if the controller simply acknowledged the proposed routing and asked to the pilot to report passing C (the exit from the zone) was this absence of a clear instruction not to enter controlled airspace somehow seen as an approvale for the proposed route through controlled airspace.
Take that to a bigger scale and in many cases, when flights report routing from xyz (small village) to abc (another small village) the controller or the FIS provider have no real idea if the proposed route takes the flight via controlled airspace or not - hence the ass covering statement required.
Far simpler I believe to remind pilots that a clearance is required and that acknowledgement of a proposed routing (the filing of a flight plan) does not provide clearance.
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Here is one often heard;
ABC123 do this that and the other
no response
ABC123 did you receive my transmission
Say again ABC123
ABC123 do this that and the other
How about simply replacing the ABC123 did you receive my transmission with "ABC123 London"
Regards,
DFC