Bad Bear,
in short no!!
If it was a case of only having A/C coming from one airfield, or even from both heathrow and gatwick, then it would have a good chance of working, as for the routes it will affect, they are roughly the same geographical starting point.
Unfortunately it is not just those airports, it is a case of integrating traffic from London City, Luton, Stansted, and Northolt as well, plus the other low lying airfields in that area that kick out the odd flight now and again.
Tied in with needing to use vectors to get A/C away from lots of different inbound routes and the holds to enable a climb, the bunching issue will still be there.
If we do not vector off the SIDs (which would go a long way to preventing bunching)
a) Heathrow and Gatwick SIDS are not separated via DET/DVR
b) A/C would get much later climbs due to A/C now coming into conflict with others that would never have been a problem before....
C) The ATCOS job becomes much more difficult because there will be lots of A/C 8 miles East of Biggin needing a climb
d) all of the above would make things less safe
Just to clarify Bad Bear, it is the taking you off the SIDS to give you a climb that is one of the main reasons for bunching, as you are vectored out of any natural stream that may have occurred. Whether you are flying at 250kts or not does not change that fact!!
The only real way to prevent bunching is for all the London TMA airfield to coordinate departures with each other..... I am not going to hold my breath as that is totally impracticable