As most have said - don't worry about the serial number. Go in with your proof of purchase that you do have and that should be enough.
As for commenting on the decision made to seize your bike - as I want there I won't! However what I would like people to consider is the fact that clearly the police thought they were doing the right thing - there is no other possible reason they would have seized the bike!
My bike was coded by the cops,but what does that prove as I haven't got the receipt although I know where I bought it from new.So what should I do,take frame numbers? What does this prove if someone decided to come up with the same allegations?
Even if I took pictures and thumb prints and posted it in the new bike thread?