Gordon Bennett, with friends like these...
Matthew, young feller me lad. You've been a bit of a twit, as you'll have gathered by now, but then again, as a young feller me lad, that's pretty much your job description. Don't take any of this too much to heart, but...
You've received two bits of 24 carat advice on this thread. I suggest you pay heed, and act accordingly.
First, contact your seller and say that unless you have a V5 in your sweaty little paw within 48 hours, the deal is off. You bought a legit bike; you have good reason to believe you haven't received one; you want your money back. If, as is more than likely, you hear nothing back, contact
ebay, saying you bought a bike in good faith, but despite numerous promises the V5 has not materialised; you therefore believe the vehicle to be illegal; and you want to cancel the deal and get your money back. You will get your money back. Ebay, as has been bemoaned many times on this forum, almost always comes down on the side of the buyer, and your case seems particularly strong. Indeed, I'd look on the non-appearance of the V5 as your undeserved get out of jail free card. If it had arrived, you'd probably have to put the thing back on ebay, which would almost certainly end up leaving a big hole in your pocket - ebay + paypal fees = 10%, give or take. You might - just might - come out of this unscathed. Which to be honest, is more than you deserve. Count your blessings, and learn from it.
Second, when you find yourself in a hole, stop digging.