Old test set, possibly ex-GPO, military or BBC, but I can't find anything about it online. There is a black fitting in the middle, which I'm guessing used to have a meter movement or rotary switch, now missing.

The engraved label says "Tester TRT 86 DGM TRT 86 ISS Open".

On the bottom of the case it is stamped "CASE NO.123A BMD/1" and in black pen it says "FBB 65/1".

The top panel is a sort of hammertone blue/grey, and the case is green, in what I think is fibreglass (GRP).

There is a row of seven GPO-switchboard-type switch keys (changeover switches?) with one cap missing, and a row of eight indicator lamps with one cover missing.

There was no case lid when I got it from a junk stall many years ago.

The fatter cloth-covered cable has a very odd plug on the end, maybe Jones-Cinch, but it doesn't fit either of the Jones-Cinch type multipin sockets on the top.

The thinner cloth-covered cable has a GPO 316 plug on the end, and there is also a 316 jack (socket) on the top.

I think it was probably used for testing switchboards or something....?

No, it doesn't work - I haven't had any way of trying it.

Might suit someone who likes ornamental old tech, or it could get repurposed as some kind of steampunk display item.