I'm not sure I understand your question.
Why do you turn the radio off before you turn the ignition off?
Vauxhall radios can normally be set to either come on with the ignition & then turn off when you turn the ignition off. Or they can be set so that you have to manually turn them on & off yourself. Without digging my audio manual out I can't tell you how to alter them .............. but it is in the manual

Then of course, irrespective of ignition, you can switch your radio on & it'll turn itself off in an hour.

Sorry Andy have't explained myself very well. The only reason I turn the radio off before I turn the ignition off is that I like my music loud but as I start work early in the morning I don't want it blaring out and upsetting the neighbours.All was well would turn radio off then in the morning start car drive away (live on quite road)once turn into main road on with radio,but it now seems to turn on as soon as I start the car doesn't matter if it was left off or on .Radio works fine in all other aspects ie as you say if I turn it on with out ignition it will turn off in about a hour . Hope I have explained better sorry if not
Even if the radio was turned up to 11, it'll start up again at a lower level.
Do you have a manual for your radio? I have the older Omega, so the head unit is nothing like yours (CCRT700), but to disable the radio coming on/off with the ignition:-
Ignition on
Switch radio off with IO key
Press the musical note & keep it pressed
Switch on radio & keep musical note pressed till it beeps