I'm very out of date here, but, from memory ....
- Companies have Letters of Agreement with Airservices detailing a lot of stuff, including performance figures.
- ATCs are trained in line with those agreements.
- If the general performance figures are changed, the Company is expected to update the Letter of Agreement
- Speeds entered into the flight plan are not entered into the software that ATC use???? I think.
So, obviously ATCs are expecting certain speeds. When they don't happen ...