I'm not sure either,only time ive seen anything to do with it was 1 day last week I started the car to go to work and temp was less than 3C And it came up with a message in the dash centre (where the digital speed, trip computers mpg readouts etc show) saying ESP on.
Other than that I haven't seen anything but like yourself I noticed I couldn't see an on/off switch like the Astra and Insignia have, its possible that it isnt switchable on the Corsa, I remember some older Astra's and Vectras not having switchable TC, it was permanently on.