Time dependant too, regardless of mileage.
Best phone a vx main dealer as they'll have the latest recommendation - started out at 80k/8yrs, I think now 30-40k.
Ask about pulleys & possibly water pump too.
Service interval is down to 40k now. If you don't have the pulleys and tensioner changed at the same time these can let go and the effect is the same as the belt snapping. If you run a 2.0sri the water pump is driven from the timing belt so any seizing or problems again can cause the cam belt to go, plus its easier to change it whilst the car is in bits.
If you run a 2.5 sri the belt and pulleys still need doing but the water pump is driven off the auxilliary belt so although a pain to change failuer will not bust the timing belt. If you have round 40k on get it done the alternative if it breaks is far worse