Sorry to contradict but this isn't the case. Knowing what the bike is worth, and deciding to keep it without reporting the find to the police will mean you commit the offence of theft by finding. All it would take would be for the details of the bike to be circulated on a briefing, and an eagle-eyed cop sees the OP riding the found bike. The serial number is checked and the bike found to be stolen. OP arrested for theft or handling, and on interview admits he didn't report it because he couldn't be bothered. To disprove a theft, the OP will have to show that he acted honestly. The offence would probably attract an adult caution, but that's still a criminal record.
If however he takes it to the station, the property clerks probably won't know what a Roubaix is, or what it's worth. They will however check the serial number against the database of lost or stolen bikes, and depending on the force will check Immobilise.com. If the owner can be traced they will contact them and get them reunited. If they can't, a bike with a buckled wheel will not go to auction, it'll go to the scrapyard.
OP, ring the local police and report the fact that you have found the bike. They will be all too pleased if you save them the trouble of storing it, by stating that you will look after it and will be willing to return it to the owner should one be found. Two possible scenarios here: one, the owner will be traced and the police will contact you, whereby you will have saved the bike from being tossed into the property store at the nick and suffering more damage. Happy owner reunited with bike through honest and bike-friendly actions of fellow cyclist.
Scenario two, you get the wheel straightened/replaced and use the bike. No owner is found and you have done all that could be reasonably expected of you to trace the owner. You win a Roubaix for the price of a repaired wheel and a phone call.
However, there is no set period in law as to how long you keep found property before it becomes yours. Theoretically it will ALWAYS belong to the original loser.