As I accepted in my earlier post, chompu, magistrates do have the powers you describe. I imagine it is exercised extremely rarely and with good reason, even when you are providing the information. There generally is no need to waste police resources arresting people for driving offences when the sentences open to the court do not require that they attend. However, I accept that magistrates do like, occasionally, to "see" a defendant before sentencing.
As for the other matter, I�ll no longer differ when you provide details of a driver who did not have his documents with him when stopped, and was subsequently successfully prosecuted for failing to produce, even though he had produced satisfactory documents within seven days.
I don�t believe that magistrates, even in the court with which you were involved, would convict such a defendant, and further, I don�t believe any such charge would ever be brought.
I was trying to provide sarah with a sensible answer based upon a sensible interpretation of the law. It's nice to see some pedantry from time to time, though!