Think you've kind of missed the point of the ATSIN. Class D/E/F and G airspace the speed limit has ALWAYS been 250kts below FL100. In class D airspace only, it may at the discretion of the CONTROLLER be relaxed provided they are certain they have a known traffic environment.
the ATSIN specifically refers to the London TMA because it is class A airspace and is a reminder to pilots and controllers alike to exercise caution when using speeds higher than those for which SID flight profiles have been designed.
Heres a link to the airspace classification rules if you cant be bothered to dust off your old Trevor Thom's.
http://www.caa.co.uk/docs/64/ATS_Classifications.pdf