I don't doubt procedures my colleagues use in the US or Canada. Bigger places, more runways, different ATC "culture" etc, and the guys there do a great job.
Vertical separation in the UK? Because its quicker to apply (Think TCAS). The conflicting SIDs from EGLL and EGKK, aren't laterally separated (by enough). They ARE vertically separated by ATC, at least initially.
Using this inbuilt vertical sepn, and some tactical vectoring aided by the 250kt limit, it may be possible to increase the movement rates for departures. Deps would all become a lot more "systemised", and a lot less "point and shoot".
Downside? Less early climbs (not above 6000ft or so for about 7-10 mins), but more unrestricted climbs once with AREA.
To reiterate, the idea is an attempt to up the departure rates and still keep things orderly (and safe). It is a big culture change for some in UK ATC, and hence the percieved difficulties. Just because somethings have always been handled a certain way or ways, it doesn't mean that you shouldn't look for other methods that may improve traffic through put.
Keep an open mind. It's a trial at moment.
Rgds BEX