[Stuart]

What's the word for a one camera set up with a screen behind? Broom cupboard or something....

'Cheap & Nasty' is the phrase you were looking for. 

The one at Millbank used by the BBC is basically a chair in front of a locked-off camera with a plasma screen behind which fills the entire background of the shot.

It doesn't have to be bigger than your living room, probably actually quite smaller.