t-f - agreed, but they do let us out of the London TMA occasionally.
Are you saying that crews are doing this IN THE TMA? I'd be suprised if anyone was 'awaiting' a computer generated descent in the London TMA.
Amongst many, frequent occurrences for me north-bound on the 'Welsh' airway when an early 'descend' call from ATC turns out to be a 'level-by'. This has also been well-aired elsewhere on PPRune, plus the comment made that Maastricht are generally good in making it clear and/or giving a required rate of descent.