(a) Where a member of the Garda Síochána has reasonable grounds for believing that a mechanically propelled vehicle to which section 18 of this Act applies has been used in a public place on a particular occasion (including a case in which the member has himself observed the use) and that the actual user of the vehicle on that occasion was a particular person, the member may, at any time not later than one month after the occasion, demand of the person the production of a test certificate in respect of the vehicle in force on the occasion and, if the person refuses or fails to produce any such certificate then and there, he shall, unless within ten days after the day on which the production was demanded he produces such certificate in person to a member of the Garda Síochána at a Garda Síochána station named by the person at the time at which the production was demanded, be guilty of an offence.
(b) In a prosecution for an offence under this subsection, it shall be presumed,
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