well - i spend my working life as a paramedic in london and i can tell you that there are no speed cameras fitted to ambulances. my employers dont have enough cash to provide us with uniform most of the time so believe me they wont be spunking any money on cameras.
tailgating any vehicle on an emergency call is not the best idea - as there are usually 2 people on ambo/panda car and the passenger can just look behind and take your plate number (if in a car obviously) - believe me it does happen.
and about overtaking an ambulance on a single carrigeway - if were on blue lights, we may think your a pr*ck but we dont have the time or inclanation to spend reporting you to anybody - provided of course you dont cause an accident or we end up attending to you a little further down the road when youve overcooked it
oh and the police and us have a good relationship - but neither of us like the brickies