"If you want to ride in the middle of the road pay road tax!"

writing a cheque for 0.0p as it's zero / low emissions, same as some cars eg. Toyota Prius (which is actually a scam of a car and does have emission and fairly poor mileage)

Ah, I see here it's done on emissions. In Oz I'm sure it was based on vehicle weight, as heavier vehicles do more damage to the roads so the magical fairy road tax was reflecting that.

http://www.direct.gov.uk/en/Motoring/OwningAVehicle/HowToTaxYourVehicle/DG_10012524

Ha! Actually the trade lic. for a bike is £66 per 12 months! :D