When on blue lights my speed is essentially unlimited (although I can still get nicked for 'dangerous driving'). My own safety, and the safety of the idiots who tend to step out in front of me tends to limit my speed though... Safety first - it'll be embarrassing to post pictures of my motor wrapped around a lamppost. If the call is for something that I think is actually serious, then I'll make a bit more of an effort to 'make progress'. I did work out my average speed on emergency calls once. I think it was 22mph. (In my own car I stick to the speed limit...)