Thanks guys - I'm just in from 12 miles - it was wet, dry, windy, calm, cool, and warm - seriously annoying weather. I chose to wear lightweight base layer under Karrimor t-shirt. Dumped the base layer after a mile, it was actually quite muggy this morning. Got showered on two or three times, soaked once, thankfully in the last two miles.
I've only got and old non-breathable, mesh sided waterproof, which ends up wetter on the inside than the outside, so I elected to leave it at home. I think I'll have to invest in a decent running jacket for winter if not before.