You are chancing getting pulled by an ANPR flag then, especially of you're SORN'ed they may just throw the book at you as what's to say you haven't been driving around the whole time....
Not worth it for a day dude
I would never drive without tax, what I am saying and have done in the past, is that you can go to a post office and get a disc 1 or 2(can't remember) days before the start of a new month and be issued a tax disc that lasts 12month +1 or 2 days =screwing the system.(But you need all your documents, hence this thread)