Hi LZ,
This assertion from the AC pilot is incorrect. The start up approval, ATC clearance, CTOT and any airfield delay is given on the Ground Movement Planning (Heathrow Delivery) frequency of 121.97. Only then is the aircraft transferred to the appropriate GMC frequency for push back authorisation. Therefore no ATC instructions should interfere with the safe operation of the aircraft. ATC route clearance is only given at a later stage if there is a re-route, or if the flight plan details are not available in the host computer for some reason. I also know of no dialogue between ATC EGLL and AC Operations concerning this subject. Perhaps someone from Air Canada would like to clarify the company's concerns.