Thanks Colin,
I have compared the specs and the main differences in models can be summerised by:
Mk I introduced in June 1990.
Mk II (from Nov 92) : As Mk I PLUS
better MPG (+1.6@75mph to 28.8)
larger tyres, from 205/65 to 225/60
larger brake disk diameter (F/R dia from 10.8/11.4 to 11.6/12.0)
Side Impact Bars
driver and pass air bags
seat belt tensioners
individually heated seats
less boot capacity down from 16.03 ft3 to 15.2
Mk III (from Jan 95) : As Mk II PLUS
restyled body, moreareodynamic (Cd down from .29 to .27)
more MPG (+0.6@75mph to 29.4)
faster acceleration to 60, (down from 8.3 s to 7.4 s)
engine compression ratio up from 10.0:1 to 10.4:1
260BHP up from 241.
torque of 269 ftlb up from 258
"Sequential" fuel injection
wheelbase increased by 3.5cm to 285cm
kerb weight of 1725kg, down by 90kg
increased boot capacity up from 15.2 ft3 to 17.0
shocks changed from gas filled to hydraulic
larger brake disk diameter (F/R dia from 11.6/12.0 12.4/12.1)
tighter turning circle 11m down to 10.6m
improved anti-corrosion protection
ABS is now Computer Controlled
high mounted rear stop lamp
Radio has RDS features
Mk IV (from Jan 98) : As Mk III PLUS
more MPG (+1mpg@75mph to 30.4)
Faster acceleration to 60, (down from 7.4 s to 6.9 s)
Engine compression up to 10.5, 280BHP, 293 ft3 and VVTi (variable vale timing)
kerb weight up ti 1815kg, up by 90kg
smaller boot capacity down from 17ft3 to 16.4
shocks now gas filled again
anti-dive suspension geometry
Vehicle Stability Control
High Intensity Discharge headlamps, auto leveling & luminance sensing
Electronic Throttle Control System
5 speed Electronicly Controlled transmission (was 4 speed)
Front seat side air bags
Much more electronic aids, sat nav & comuter etc.
So now my buying experience is going to be a much better informed one.