As Hopkirk states, 'producers' are very rarely issued these days because modern technology means that it's easy enough to check on the relevant driver and vehicle details directly anyway.
Further, the use of 'producers' can cause great inconvenience for (often entirely innocent) motorists because it can be hard for them to get to a police station during opening hours. (Here in Suffolk there are only three police stations open to the public across the whole of the county and they only open, from Monday to Saturday, during office hours. If, say, a motorist was involved in an accident which took his car off the road, it could take him several hours by bus to get a police station).