As per the title, I have managed to add cruise control to my MK5 Astra SRI. It was simply a case of getting the stalk changed and then a Tech 2. Total of about 10 Min's work.
I assume that it can be done on the higher spec models of Astra, with the clutch switch mentioned in other cruise control threads.
I paid around £30 for the stalk, and am very happy!
I work at a Vauxhall dealer, and thanks to the AOC, now they know it can be done!