In the phraseology section of our manual:
"Expedite climb/descent"
To require a pilot to climb/descend at best rate.
It is stressed to all trainees that the phrase should not be over-used, on the basis that if pilots hear it all day, every day, their response to it may become less urgent. Controllers should have an idea of what an aircraft can achieve in an expedited climb, and should also know what sort of aircraft should not be told to expedite.
Where at all possible, best practice is for controllers to solve the conflict vertically (climb underneath, descend on top), by using headings (conflicting aircraft to miss by 3 or 5nm), or by using a "level by" restriction, eg "Climb FL370, level by XXXXX", or "Climb FL370, cross XXXXX FL340 or above". Naturally, if a pilot cannot make the stated restriction, we expect that s/he will tell us - but not all do!
I don't know anyone that overuses the phrase "expedite", but then I don't work at TC!
I'm not sure about "commercial pressure" affecting ATCOs - our job should be primarily about safety, and as such excessive use of "expedite" is more likely to be frowned upon than encouraged.
LTP