2011-04-16 Sat 9pm - London Marathon Ride

Up to 30 minutes FREE
Up to an hour £1
Up to one and a half hours £4
Up to two hours £6
Up to two and a half hours £10
Up to three hours £15
Up to six hours £35
Up to 24 hours (maximum) £50

looks like it'd be £35 / £15 + £1.

spoke to some people and it looks like it won't be easy, as you used your credit/debit card to get the bike and not your membership key.