I'm not aware that the price is negotiable in the UK, and according to the price list, Ford extended warranty plans can be purchased any time up until the vehicle's first date of registration.
I purchased mine when I bought the car.
They're at it then cos it should be £590 - http://www.ford.co.uk/Buyingandprot...rsServicingandExtendedRoadsideAssistancePlansFord quoted me £915 for three services.
I told them to poke it.