Agree 1972 Commer - has 71-72 J plate; the linked one seems accurate as a similar 74 on an M plate. 7.5 tons may be correct, but not PB - that was a fair bit smaller. Coachbuilt body but no idea at the moment (away from home so can't check books), but Marshalls of Cambridge did a lot of horsey taxis, and so did Lambourn but this is smaller than the illustrated Commer Commanders' Plus probably several other coachbuilders.

Which is where I run out of steam ....