"My wife thinks that if we have no answer/reply by 30th she will be an 'illegal alien' as she puts it."

Russ the official line from the home office is this:

Your immigration status while your application is being decided
If you make a valid application before your permission to stay ends, your existing immigration status will continue until your application is decided, even if the decision is not made until after the end of your permitted stay. If your existing visa or other permission to stay here allows you to work, you can continue to do so until your case is decided.

My wife just recieved her FLR last week and it took 21 days from posting until it arrived back...Tell ur wife not to panic.