I believe that London Control has this feature which enables them to display the selected MCP (Mode Control Panel) speed, altitude and more.
I was told by a fellow pilot working for another airline that his captain mentioned that when ATC give him the speed restrictions such as 210 he dials this into the MCP "too keep the controller happy" and then proceed to descend at a faster speed. Now obviously if the controller wanted to enforce it strictly he could determine the speed difference from the ground speed if not the actual IAS if thats even possible but i digress.
This feature also has the benefit to prevent alt busts, especially the ones where pilots read back the correct cleared level and then dial up an incorrect level on the MCP.
Initially I thought what he said had to be a mistake, but after speaking with some controllers they said that despite this technology not being available in all UK centers that London certainly had it. Impressive to say the least.
On a different note could an controller enlighten me as to why there is not a better way to find out what cruising level is to be used by a particular flight. I often get calls asking whats our final level is, or prompting it in anticipation of being asked over the RT. Surly with the current data link technology and flight processing stripes I would have assumed that this information was available to controllers. Are you just confirming it with us or do you not know to start with?
I know that these levels can often change depending on the FMS optimal cruise level on the day as well as weather, commercial or traffic factors against the flight plan, perhaps this is why it is confirmed by ATC. Anyone?