Well, after a whole lot of off-roading on the weekend I gave the car a very thorough cleaning down. In the process of cleaning the rims off I gave the brakes a good blast too...

To my surprise the noise has gone away which lends a lot of weight to the suggestion the noise is coming from the brake pads moving in the block a little.

It seems to make sense that as you apply the brakes, the pads maybe move a little, then as I corner and release the brakes they "Clunk clunk" pack into position.

The brakes squeel has also gone.

Worth a try as it cot nothing!