Reasons why the 1.8 beast won't start in winter are plentiful....

temperature sensor (can be checked with a multimeter)
faulty ignition coil (cracks on insulation), possibly dizzy cap and rotor can cause it too but you would have issues also when warm
cracked/perished rubber mount under injector unit
faulty throttle actuator (gears missing), this would also effect warm idle but much more prominent on cold engine
where in Bristol are you? Might be able to have a look at it Monday (down in Devon for work).