Cam Belt Change

[BigV]

My 2008 Passat is now 4 years old this month and has less than 40k on the clock. I've been advised by VW that the belt needs changing now rather than wait for the 60k mark. They've quoted me £410 which actually isn't too bad and falls in line with a couple of independent quotes I've had. I've never had a belt change done on a car before based on the age of the vehicle and always waited for mileage to clock round. Is this VW trying to charge for work not strictly necessary yet or is it a must do job at 4 years old regardless of mileage.

Thanks

Martin