i think the police personnel are confusing the legal requirement on drivers "of mechanically propelled vehicles" to report where details have not been exchanged "(a) must do so at a police station or to a constable, and
(

must do so as soon as is reasonably practicable and, in any case, within twenty-four hours of the occurrence of the accident." The drivers failure to do so is a breach of RTA.
Source:
http://www.dft.gov.uk/collisionreporting/Law/default.asp
There is more:
http://www.askthe.police.uk/content/Q585.htm
Here, they comment that not all police forces will accept a report after 24 hours. Seems debatable: a way of massaging crime numbers perhaps, and an invitation to hit and run merchants to avoid detection. How that applies to a cyclist who is a victim of a hit/run is debatable. The second para. of the reference above states:
"Most crimes do not have a time limit on for reporting them
The crimes that do have time limits are summary only which means that they can only be tried at a Magistrates Court so are relatively minor offences, they must be prosecuted within 6 months (e.g. common assault, harassment and take without owners consent (TWOC))."
That should give them something to chew on! Suggest the OP puts matter in writing and asks them to pursue the drivers breach of RTA.