§ Mr. Edgeasked the Secretary of State for the Home Department what the margin of error of the breathalyser is in detecting whether a driver has more than the legally permitted limit of alcohol in his blood.
§ Dr. SummerskillThe overall margin of error for the device, which of course 293W serves only as a preliminary check, varies in value over the blood alcohol concentration range. Where the concentration is above the prescribed limit, the device invariably gives a positive indication. Below but near the prescribed limit, false positive readings may be obtained. Apparent discrepancies between the indications of the device and the laboratory analysis of a specimen of blood or urine may be due to factors other than variation in the performance of the device. If my hon. Friend would like further information my noble Friend the Minister of State will be glad to supply it.