Quick update:
I set myself a target of raising 50 pounds - so far, I've had 25 as online sponsorship and 14 on my actual form, so that's 78% of my target. If I then add the 25 quid that my wee chum has managed to badger my old colleagues into pledging, that that makes 64, which would be 108%.
As long as I don't actually die during the run, that's not bad at all