I dont think it applies , for the older cars . As far as i can gather they are only increasing band 'g' cars . Mk3's are before 2001 so go on the standard tax rate which i believe to have risen slightly.
thats wat i thought... the new band only applies to new cars, this is wat ive found of t'internet
"In his Budget last year the Chancellor created a new top band G of vehicle excise duty for new cars with emissions over 225 grams per kilometre. At £210 a year this was £20 higher than the next band. Those in the band  labelled the Chelsea Tractors  include BMW X5s and Range Rovers. At present there are 225,000 of them.
Mr Brown made plain that the new band was not retrospective and did not apply to 4x4s and other heavily emitting cars bought before last April. They were put into Band F and will remain there."
i think the current tax prices are increasing slightly... but you boyo's with v6's wont end up paying £400 as it should only go up £20 - £30!
i hope.