Wow Notso you have real bee about something! There are laid down proceedures with all emergency services and that is not negociable. I wonder what you do as a job?
In central london, An incident at Parliament I believe is a twelve engine call out. As far as I know even if it is a chip pan fire! I suspect some engines get stood down en route and I am sure some ambulances did in the situation you have got bogged down with. The purposes sometimes of callouts is to rehearse for the one when it does go wrong. Drivers not used to the route at speed. Roads have been changed since the last time etc. etc.