oiltreader:
This is begging for a caption, so come on have a go.
oily
My caption would be unprintable because I did that back in about '65.
I had a 6 wheeler AEC of Wimpeys working on building the MI near Nottingham. The lever to release the tailgate was on the front of the body so you only had to reach out of the cab as the body went up. I’d done it so many times that - I forgot. 
Of course I wasn’t going to climb up the body to pull the lever so took a big hammer and started whacking away at the hooks at the back. When they released the load came out with a rush and the front wheels bounced back to the ground, narrowly missing the banksman who, never having seen underneath a lorry before, was regarding the sump with interest. 
Lawrence is right about the P & S Macks. I was working for Ilkeston Haulage at the time and was often passed by them all lit up like christmas trees (we called them that) coming down the A 74 at night.
Another one shot over the Heads of the Valleys passing me (and that was the old road) with hardly a sigh.
My memory though is that they were more orange than yellow, but I could be wrong.
I think most if not all of them were right hand drive imports from Australia, where a year or 2 later I had one of my own pulling 3 trailers. 