Merely a pilots input here, so I don't have the vast airspace depth of knowledge of the TC/AC controllers regarding daily issues created by this.
Personally I can't really see how 'bunching' will improve purely by limiting LTMA departures to 250kt. I fully accept that 'bunching' is a major issue - and always has been. I'm just not really sure that this is the answer to it. Slot tolerance across all departures is far more critical, as is mix of traffic from ALL uk airfields to an exit fix. A take-off just one or two minutes creates, or cures the problem on many occasions. This of course can never be calculated, predicted, with mix of traffic from various points all under different variables.
Can someone confirm also that this applies ONLY to LL/KK/GW/SS departures. I presume BB depatures for example into COWLY/WELIN are uneffected by this trial??
Rgds
30W