The campaign to raise the needed money started yesterday, 21st of October. The plan was to perhaps raise as much as 5500 pounds by the end of the year; Richard Dawkins pledged to match any donations up to that amount. That would give the campaign £11000, enough to run an advertisement ("There's probably no God. Now stop worrying and enjoy your life.") on 30 buses for four weeks.
The donation page has been open for only a day now but the amount donated already stands at £50000, almost ten times the original expectation - and that's before the £5500 Dawkins is pitching in - and it's still climbing. I'd say there's a fairly significant untapped constituency there for any politician willing to stick their neck out in defiance of religious groups. The campaign website is here, and the donation page is here.