The magistrates had erred in exercising their discretion under s.78 Police and Criminal Evidence Act 1984 to exclude roadside breath tests and those taken at the police station where there had been a mere technical breach of the roadside test procedure.Appeal by way of case stated by the Director of Public Prosecutions ('DPP') against the decision of Sale Magistrates' Court on 2 April 2003 to acquit the respondent ('K') of driving whilst the proportion of alcohol in his breath exceeded the prescribed limit. K had been stopped and was subject to an initial roadside breath test with a Lion Intoximeter SL400A. On that first test an illuminator on the device activated indicating that a second test was required. K undertook a second roadside breath test without the mouthpiece on the device being changed. The second test was positive and K was arrested and taken to the police station where further tests were positive. At trial K was acquitted on the basis that the manufacturer's instructions for the device had not been followed in that it had not been correctly assembled because the mouthpiece had not been changed for the second roadside breath test. Accordingly, the Court excluded the evidence of the roadside breath tests and those taken at the police station under s.78 Police and Criminal Evidence Act 1984. On appeal the DPP argued that: (i) the manufacturer's instructions did not require the mouthpiece to be changed after each use; (ii) in any event, a technical breach of the roadside breath test did not invalidate the whole procedure; (iii) equally, such a breach did not invalidate the positive samples taken at the police station and such evidence should not have been held to be inadmissible; and (iv) even if the magistrates had been entitled to come to the view that the device had been incorrectly assembled, the decision to exercise their discretion under s.78 of the Act had no basis and was perverse.HELD: (1) On a proper examination of the instructions of the device, there was no requirement to change the mouthpiece for a second roadside breath test by the same person and the magistrates had not been entitled to find to the contrary. In any event it was obvious that such a second test's result could not be distorted by the first test. There was accordingly no basis for the magistrates' conclusion that the device was not correctly assembled or that the roadside breath test had not been carried out correctly. (2) Moreover, even if there had been no right to arrest K because there had not been a proper road side breath test that would not be sufficient to allow the magistrates to exclude the evidence of the tests at the police station Fox v Chief Constable of Gwent (1985) RTR 337 considered). If that were not the case a correct roadside breath test would be a condition precedent to a conviction for drink driving. (3) In those circumstances, even if the magistrates had been correct to hold that the mouthpiece was required to be changed they had erred in failing to properly consider the fact that even if the mouthpiece had not been changed it would not have affected the admissibility of the later evidence and therefore the result. (4) It was to be noted that in order for the magistrates to exercise their discretion under s.78 of the Act to exclude a road side breath test there was required to be something more than a mere technical breach of the roadside test procedure. Justices were required to weigh the defect and consider its effect on the evidence of the samples given at the police station (Director of Public Prosecutions v Kay (1999) RTR 109 considered). In this case even if the magistrates had been correct to hold that the mouthpiece should be replaced, there was nothing more that would justify the exercise of their discretion under s.78 of the Act.Appeal allowed.