Re: Any idea what this is ?

[Roger Plackett]

Yup, they are the Continental smaller-than-car-cigarette-lighter-plug 12v sockets, into which you can plug a 12v lamp, or a 12v hairdryer – as sold at chandleries (useless, in my experience), a 12v charger for a mobile phone, and anything else which needs 12 volts. The centre contact is positive, and the ‘skirt’ is negative. They may have their own fuse in the central fuse board.