On a 2018 M5, though I think it's the same regardless of age/model.
Under 60k miles: £1987.00 per year with £100 excess.
Over 60k miles: £4783.00 per year with £100 excess.
Blimey that’s a considerable chunk more. Also, the Mercedes extended warranty doesn’t require an excess and is the same price up to 100k miles.
That said, I think Mercedes make up their money on servicing costs as that seems to cost more