I got the bugger out. Recovered the screw, and put it back in while it was out of the car just in case I dropped it again! Gave it a clean while it was out too.

You were right about it being a pain in the azz. But its all back in now, and it looks like it might be somewhere near where it needs to be too. Fingers crossed that it all works ok when the new cap and rotor turn up.