So I went and had a look at the 40k mile ST2 and ended up getting it. It drove so nicely on the test drive and seemed in very good nick and was essentially exactly what I was after.
Highlights;
2006 ST2
Completely standard
40k
Full history
Fresh MOT
I got it from a Ford main dealer (had come in in PX against an ST diesel I believe) so it had some bits done in their workshop, full service and a year warranty.
So far so good! Obviously its a completely different experience to my previous car, an E46 330d, but I'm definitely enjoying the change and it feels good to be back in a Ford after some time out!