"Chirping" Aux belt

[C.A.R.]

Near the top of the engine, there is a large pulley. I've no idea what this is attached to as I haven't had much of a look at the engine since buying the car (could be power steering pump?!)

Basically after a spirited drive down some b-roads yesterday the car developed this chirping which is constant regardless of speed (which led me to believe it was the Aux belt). Looking under the bonnet it's coming from the location described above.

Any ideas what it might be? Tensioner?

Father in law is going to crease up. 1 week in and I already need him to look at my French car because it's making a strange noise!

EDIT - have a video...