In the London TMA, aircraft are supposed to be Enhanced Mode S rather than just Elementary Mode S.
The information downliked by the Mode S radar heads is (avionics permitting):
MCP / FCU Selected Altitude
FMS Selected Altitude
The above are the only "intent" parameters. All the rest are "actuals" as follows:
Heading
IAS
TAS
Mach
Vertical Rate
Roll Angle
Track
Track Angle Rate
Ground Speed
Many of these are for "future use" either for display to the controller or to improve the radar tracking and prediction capabilities. However MCP Selected Altitude is currently being provided to controllers and I understand is considered by some to be the best thing since Mode A/C.