At the time you mention Bristol had two AEC TLs and an ERF HP. The HP pictured was transferred to Kingswood, a suburb of Bristol but actually in Gloucestershire, it was absorbed into Avon in 1974.
This looks like a canopy cab - a short-lived idea which was to be seen on both Dennis and Merryweather turntable ladder chassis in the early and mid 1950s.
It had a back to the cab with a sliding door access to the crew compartment, Avon transferred the appliance to A3 Avonmouth where it remained until disposal in the late 70s.
Added by Rob Johnson on 17 November 2018.