Recently a motorist was allegedly caught speeding on an LTI 20-20 in Somerset. He applied for evidence and requested moving the case from Taunton to his local Magistrates court.
CPS replied they would move the case to his requested court and also notified him they would not be continuing the case due to lack of evidence.
It seems requesting the evidence, if done properly, results in case dropped probably due to the fact that the equipment could not be proved to be working correctly or not used correctly.