I see that NATS have implemented a maximum rate of climb for civilian aircraft in the London and Scottish FIR/UIRs of 8,000fpm in class A to E airspace.
This came into force on 5th July 2007 and was partly as a result of an investigation into a near miss where TCAS couldn't keep up with the closing rates.
http://www.airproxboard.org.uk/docs/423/2003.pdf