Some of them in the early 50's to my recollection were Guy Half Cabs which dated from the 30's and were pressed into service when there was a shortage of vehicles because of breakdowns. Even in the sixties they and a Leyland equivalent were regulars on the Workmen's specials which picked up by the County. Here is a pic of one in the livery of Burton on Trent. You will notice that this had a rear door. Those for Northern had a coachbuilt front sliding door.