Can anybody please help me identify a plug socket

I’ve recently acquired an Acorn Audio Comparator which is an old box that allows you to route between audio sources, amos and speakers in any configuration. The problem is that I can’t identify the input sockets on the back and can’t find the corresponding connector.

I think the mains socket is a Bulgin 3 pin but it’s the round metal sleeved sockets I’d like to know about. If anyone can help I’d be very grateful.

https://photos.app.goo.gl/cNPPBJmNJCK8YSPe6

Many thanks

John