I think this bird was a little too big for a Thornbill though, my first reaction was a smallish and slightly odd looking Rufous Whistler (which it isn't of course) but it does have a slightly rufous tint to the breast. I have one other picture with a similar view to this one, but no better view of the face unfortunately, as well as two different views which I have attached.
I think there's too much colour in it for a Jacky Winter (on the underparts), but then again, I haven't seen a Jacky Winter in WA and maybe they do have a bit of colour.
I thought I'd replied to this but I must have forgotten. Yep, this has gone down as an unknown, one of pleasingly very few in my time in Australia so far.
Thanks for the suggestions though.