In reply to Dave Williams: Apologies if this has already been responded to but I have not read all the messages.
By law a constable can require you to produce your driving licence if you are driving a motor vehicle on the road (see below). It has never secretly become mandatory. The producer merely is a nicer way of you proving that you have a licence, rather than being prosecuted for not carrying it with you.
Section 164 of the Road Traffic Act 1988 provides constables with a power to require the production of a driving licence and in certain cases a date of birth.
164(1) Any of the following persons -
(a) a person driving a motor vehicle on a road,
(b) a person whom a police constable (see note below) or vehicle examiner has reasonable cause to believe to have been the driver of a motor vehicle at a time when an accident occurred owing to its presence on a road,
(c) a person whom a constable or vehicle examiner has reasonable cause to believe to have committed an offence in relation to the use of a motor vehicle on a road, or
(d) a person -
(i) who supervises the holder of a provisional licence while the holder is driving a motor vehicle on a road, or
(ii) whom a constable or vehicle examiner has reasonable cause to believe was supervising the holder of a provisional licence while driving, at a time when an accident occurred owing to the presence of the vehicle on a road or at a time when an offence is suspected of having been committed by the holder of the provisional licence in relation to the use of the vehicle on a road,
must, on being so required by a constable or vehicle examiner, produce his licence and its counterpart for examination, so as to enable the constable or vehicle examiner to ascertain the name and address of the holder of the licence, the date of issue, and the authority by which they were issued.
164(2) A person required by a constable under subsection (1) to produce his licence must in prescribed circumstances, on being so required by the constable, state his date of birth.