"In that case, I told them quickly, because I didn't want them blaming me for anything! I sent it registered post."
Wise move. When you leave a company, you want to make sure that your have given up all of your keys, codes and accounts on their computers. You also want to be receipted on that as well. Be sure to insist on that if before you agree to an exit interview, if they do that, or sign any documents.
If you don't need access to something as a part of your job, don't get keys/codes for it. It can be very unpleasant to have to answer a bunch of questions regarding a crime or breach in an area that isn't part of your normal activities. Get one time or temp access when you need it. If it's a secure area, get somebody responsible to walk you in and check you out or even sit there while you do your work. Even if they deactivate a key card or company ID, make sure you give it back and get a receipt.
Biting the hand that feeds IT
