In reply to muppetfilter:
I agree with your frustration, but....
We may just be able to justify a stop and search, and we might even be able to justify seizing the bike. We then have the issue of proving it is stolen and who the owner is. If as you say it has been repainted, a few bits have been moved around and a serial number has been filed off - we are going to struggle to prove he didn't "just buy it off some lad second hand."
At which point he gets his bike back and we have wasted a lot of time.
Conversely, were you to be stopped on your racer, and because you can't produce a receipt you were arrested and your bike was seized, I don't think you would be too happy with the police either.