This is the Composite Video connector at the back of every Beeb. It is a BNC-type connector. I've never understood the point of these as all that ever seems to happen is that you need an adapter to convert it into something more sensible which you have a lead for. So, this being no exception, the Composite Video socket has a BNC-to-Phono adapter and a Phono plug attached to that.
The other end of the lead is a second Phono plug which goes into the "CVBS In" socket at the back of the DVD recorder.