It's not a matter of £1BN to extend the life of the airframe from 2013 to 2018 - the cost is the overall cost of operating the aircraft to 2018. The aircraft can post GR.9 modification happily go past 2018. It should be remembered that not all Harriers at at high hours. What I see as far more realistic is a rethink of JFH and the aircraft being dedicated to Naval operations perhaps in the form of two operating Squadrons with a large number of aircraft being kept at operational readiness but as war reserve.