So I just rang the DVLA to double check the price of my tax for 6 months an for a year With the engine increase from a 1400 to 1800. They said that there is NO increase and my tax still stands at £93.60 for 6 months or £170 for the year. I hung up and thought that seems too good to be true and the last thing I want is to have my car taken off me for "tax evasion" so I rang back up.
He said because my car was registered in march 2001 (when the rules changed) the emissions on record from factory are set for life, therefore being correct and my tax does not increase at all.
If my car was regitered a day earlier or started out as a GTi it would been around the £135 mark for 6 months!
RESULT!