I think I'm ready. I've got 3 spare inner tubes, a puncture repair kit, lovely new cycling top (courtesy of Practical Action), all the gear.
Please stop raining.
(obligatory 'please sponsor me' bit: http://uk.virginmoneygiving.com/dakegra)
 looks like obsessively checking weather for London is working. Rain not expected until 7am Sunday, by which time we should be finished...