Even in jurisdictions where police make recordings, they use the recording to prepare their notes and then dispose of the recording.

This is an excellent video to watch in its entirety, but at 45:30 you can see a police officer proudly explain that he destroys recordings after he gets what he wants from them:

http://www.youtube.com/watch?v=6wXkI4t7nuc

This might help explain the reason to have your own recording.