Young Paul,
On the subject of SID tracks and departure spacings, as others have mentioned above, it's a compromise between what the operators want (expedition), what the local residents want (quiet), and other bits such as R/T fail separations. The really busy units have immediate turns after departure (watch those 747s out of LHR!) but the quiter airports, I suspect, would have a heck of a job with local residents, in trying to alter SID tracks (although as one house gets overflown more, surely another gets less noise?). Never mind the argument that a 737 sitting on the runway for 4 minutes awaiting departure behind an ATP or SF34, is burning 4 minutes worth of fuel into the environment....
I have seen EDI operating with a large industrial fire on the 24 climbout (huge black smoke column about 2 miles out) - for safety, all props went immediate left and all jets immediate right.
1-minute separations really got things moving!!!
As A-R says, if you get the chance, you'd be very welcome as a 'customer' to visit ScATCC/GLA/EDI. We're delighted to hear how to improve our service to crews, especially if you bring biscuits...