Where a person is convicted of an offence by a court of summary jurisdictionF1. . . , and it is proved to the satisfaction of the court, on oath or by affidavit or in the prescribed manner, that not less than seven days previously a notice was served on the accused in the prescribed form and manner specifying any alleged previous conviction of the accused of an offence proposed to be brought to the notice of the court in the event of his conviction of the offence charged, and the accused is not present in person before the court, the court may take account of any such previous conviction so specified as if the accused had appeared and admitted it.