In reply to ebygomm:
FYI with Economy Car Hire the "included" bit may now include less than when you have booked with them; it is an additional £16 for "Worry-free car rental with our enhanced top-up insurance provides cover against any loss or damage to the vehicle not covered by the car rental insurance including wheels, tyres, glass, under body, roof, interior, keys, locks and misfuelling. In the event of a loss you will have to pay our car rental partner directly and then claim the amount back from our insurance provider. The car hire supplier may offer their own alternative optional insurance product."
So it looks like they've now lumped the tyres, glass, underbody (etc) in with the keys and "misfuelling" whatever that is.
Still probably the best deal for us on this trip so thanks again for the tip.