<<Also could somebody confirm (for example in London TMA) when ATC considers an aircraft to not having performed a CDA... I'm pretty sure you are allowed to fly level for a while (2-3miles??) before there is a trigger of non CDA compliance.. >>
I retired a while back but, so far as I know, ATC is not concerned whether a pilot flies the CDA as long as he complies with ATC instructions. (Because of other traffic it's often not possible to fly CDAs anyway) However, the airport authority has some means of determining whether aircraft have flown CDAs. What action they can take I do not know.