6. For the purposes of Article 3, a certificate purporting to be signed by the governor or deputy governor of a prison or young offenders centre which specifies—
(a)the date on which a person was discharged from prison or a young offenders centre;
(b)the sentence or term which the person was serving at the time of his discharge, the offence in respect of which the sentence or term was imposed and the date on which he was convicted of that offence;
(c)the date on which the person would, but for his discharge in pursuance of prison rules, have been discharged from prison or a young offenders centre,
shall be evidence of the matters so specified.