classic motorcycle forum

Hi , I am hoping someone can help ? I am try to find out what bike my dad used to ride when he was I the army , He was I  the army in the mid 50s 'Amd served in the royal signals And rode in the trials team , I have attached a couple of pictures of him on a bike , I cannot seem to find anything that matches ? I thought he rode a matchless , but the picture shows the exhaust on the left of the bike , most or all the matchless seem to have the exhaust on the left ? Any help would be much appreciated, many Thanks matt