Turntables are actually quite unusual outside loco depots that have tender engines, or sometimes close to major termini. I actually can't think of any industrial premises that had them. It's a turntable for turning locos round, not as in a roundhouse for distributing them to multiple radiating tracks. It also appears to have no turning mechanism; now "hand-push" tables were not unknown, but there don't even appear to be the handrails associated with those.
It's a big gasworks and normally on such an internal railway with their own small locos and lots of ground, a triangle would suffice for any turning rather than the expense of a turntable.
I see Myers were a coal & coke merchant. They would have to collect the coke from somewhere, and a coke works is the obvious place. Major gasworks took coal in and generated a range of products from it, gas obviously, but also coke, tar, and some chemicals. Some of the coke was then used in fuelling the process, but more was sold. Wagons with "M R" on them were extremely common, this being the Midland Railway, who I believe had the largest mineral wagon stock of all, and a private company would have to avoid that label.
That the company named on the wagon was renamed some years beforehand is nothing; at nationalisation in 1948 there were still plenty of wagons with pre-grouping names on them; it woud only get changed at (infrequent) full repaints.
Why does the track approaching the turntable appear to have a third rail in the centre of it?
A good mystery.
