There is no such thing as Road Tax, though the Advertising Standards Authority doesn't object to car advertisers using the term.
Some motorists strop about cyclists not paying road tax and object to them using the roads. The reality is that roads are paid for out of general taxation, such as council tax.
Anyway, motorists actually pay Vehicle Excise Duty (VED) based on their vehicle's CO2 emissions, so a cyclists would pay £0 even if they had to pay.
But, for a moment, let's pretend Road Tax to spend on roads exists and raises the money that VED raises.
In 2009 government revenue from VED was £5.63bn.
I don't know how much gets spent on roads each year, but I do know that the 2009 contract just to widen a mere 22 miles of the M25 motorway (which cyclists can't use) was £3.4bn
'War on the Motorist'? I don't think so.
Mind you, I can't help but feel that a better use of that cash would have been to build a splendid motor-traffic free cycle route along the south bank of the Thames.