Cars registered before 1st March 2001 are not taxed on their CO2 emissions but rather their engine capacity.
The current rates are:
1549cc and below - �120 (year) or �66 (6 mths)
Over 1549cc - �185 (year) or �101.75 (6 mths)
Your car obviously falls into the higher band.
The Government has not announced future increases ahead of the relevant Budgets (unlike for the CO2 tax rates) but are likely to increase in line with inflation. This year the increase was �5 (12 mths).