Hi Paul,
I did an unofficial investigation into your case and the situation was exactly as I had thought. There was a backlog due to LVPs in the morning; there were a lot of aircraft that had been delayed and although you could have physically made it to the holding point to make your CTOT, you would have penalised other aircraft in the queue. Heathrow ATC have to take a wider view of the situation and try to be fair to all operators in these circumstances, to provide the most expeditious and efficient departure rate. The situation was compounded by the runway alternation at 1500. I am sorry that you lost out on this occasion, but I am sure you will agree that the delay you suffered was not excessive. In the future if you suspect that there may be airfield delays, contact GMP as soon as you are ready and book your place in the departure queue. If you wish to discuss this further then please contact me again.