Just spoke to a 180 owner .... who has changed just the main belt, and left the others - said they were ok - sound plausible? Why would you do this?
FAQ
Cambelts are due at either 90,000 miles or 6 years, whichever comes soonest. There are 3 off belts here. Prices range from £350 upwards. If the car in question has no indication of a belt change be wary or negotiate the price down by around £600. If that doesn’t work, walk away!