You got yourself a very nice bookcase there. Looking at the colour, I would say it’s mahogany, although possibly oak or teak. Most certainly made somewhere in the 1950s. It is a type of bookcase usually made for lawyers and alike, often called Barrister bookcases (as you mentioned, Lawyer’s bookcase). This is due to the fact these cabinets were made to stack, so easy to transport in sections. During the 50s/60s they became more popular for regular use.
I do however doubt this bookcase was made by Robson and Sons, considering the modern style, as well as lack of trade mark they would have left. This is not to say this bookcase could not have originated from a furniture store/upholstery in Ponteland. The name Robson is very common of course and still present, even in this trade.
After some research, I think it is very likely you have a ‘Simplex’ bookcase, although I could be wrong. They were founded in 1935 and as far as I know, still active.
I found a very similar bookcase shown below, although there appear to be some minor differences.
There are however similar furniture retailers, like Minty ltd, Library specialists, Oxford.
Nice find none the less, and the marking on the back is certainly intriguing. You could of course ask the previous owner, to possibly find out more