The annual service (every 12 months or 12,000 miles, whichever comes first) is very important. In fact, I'd argue it's even more important for low-mileage cars that spend long periods parked up doing nothing (as the service will check the steering, suspension, wheels, tyres, exhaust and fluids).

Oil can lose its lubricity over time, and I would change it (and the filter) every 12 months.