Puma v Mi 17 v Blackhawks
On 28 October 2008 the Royal Thai Army announced a deal to buy 6 Mi-17s to meet its requirement for a medium-lift helicopter. This is the first time the Thai military has acquired Russian aircraft instead of American.[6] Flight International quotes the Thai army’s rationale: "We are buying three Mi-17 helicopters for the price of one Black Hawk. The Mi-17 can also carry more than 30 troops, while the Black Hawk could carry only 13 soldiers. These were the key factors behind the decision."[7]
Actually I think £339 million would buy more capability for hot/high ops than a Puma Upgrade.
Lastly must we always go down this route after decades of service. Would the RAF have considered a Spitfire upgrade 40 years after its first flight?