why would the police be the only authority to hold details of crashes?
They are not--there has been work done by the Transport Research Laboratory which has had a project of attending crashes whenever possible and recording them. However, the police are the most consistently-resourced to do this and they obviously have statutory duties, too. There has been a lot of criticism of the STATS19 system used by police to record crashes; it is a pretty tall order for a PC on the scene to accurately record a crash just from on-the-spot witness statements etc.
They are not--there has been work done by the Transport Research Laboratory which has had a project of attending crashes whenever possible and recording them. However, the police are the most consistently-resourced to do this and they obviously have statutory duties, too. There has been a lot of criticism of the STATS19 system used by police to record crashes; it is a pretty tall order for a PC on the scene to accurately record a crash just from on-the-spot witness statements etc.