Nobody has mentioned D&D on 121.5. They are not, as someone once said, "Detect&Destroy", but are geared up for just this sort of occurrence. If you KNOW you have infringed CAS, then get the hell out of there by the shortest route and call the relevant agency if you know it. Even if it was only a couple of miles, call them and tell them it was you and APOLOGISE. Chances are a) they WILL have noticed your incursion and b) if they have not had to move their traffic out of our way you will get asked to phone in for a discussion and that should be the end of it.
If you do not know for sure either where you are or whether you have infringed, I would suggest a call to D&D. They will immediately give you a position and ensure you are not in the wrong place. If you are, they will help you get out and liaise with the relevant agency. The use of 0030 squawk I would suggest should be reserved for its proper use, which is when the FIR 'controller' is talking to an aircraft who is uncertain of position and he wants D&D to help him find it. The willy-nilly selection of it will mislead radar controllers as they will assume the FIR are in contact with you and they might not be.
The bit about trying to hide is very true. You won't do it and you will definitely get the book thrown at you. There was a discussion about this on the GA /Forum under the title of "Please squawk Mode C..." or something.
Best of all, make sure your navigation is up to scratch and then you won't need any of this.
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"Take-off is optional, Landing is mandatory"