Thanks Harry & Emily's dad.
I take your advice on board.
It's a shame I can't find a good garage near me in the north west (independent or dealer).
If I take the "age or mileage, whichever comes first" approach then yes, 2 of the 3 dealers were right.
So I can't understand why the 3rd dealer I've asked, which is the one who did the (5 years full service when the car was 7 years old) service last year, says I just need a basic mini service? Maybe it's in line with what Emily's Dad says i.e. my very low mileage means hardly anything needs servicing. But then surely that's contravening the manufacturer's stated 8 years interval?
FYI the difference between the basic mini service and the 8 years full service is that the 8 years one includes a new Air Filter, the wheels off and checked, the air con checked (not fixed, just looked at) and a better quality