I agree with all that has been said on this post so far, but I can update you on where CDAs are either in force, or will be coming soon.
Currently Heathrow, Gatwick, Stansted, Luton, Bristol,Cardiff, Manchester (but only at night, when will they go H24), Birmingham (just starting night time only), Newcastle
Soon to follow are hopefully Edinburgh, Glasgow, Aberdeen, Southampton (albeit may be runway specific), Belfast Aldergrove, Liverpool, Doncaster
For information CDAs should be attempted at all times and the London airports all have monitoring that send reports to ATC for performance reporting amongst the watches.
The Arrivals Code of Practice can be found at:
http://www.dft.gov.uk/pgr/aviation/e...odeofpractice/
You may also be interested in this for a European view:
http://www.eurocontrol.int/environme...20brochure.pdf