"If the platform is capable of medium range civilian search, and capable of detecting Russian subs, that's the minimum spec fulfilled. It might not be the best, but if it does the job it's still better than no capability, and it frees up funds for other requirements."
TA, even the old P-3 did a hell of a lot more than sniffing subs, it's only one of a dozen missions. They were used a lot in astan and Iraq and there wasn't many subs there.
UK can buy into the P-8A or buy the ****tiest thing out there. The fleet cost over 30 years isn't that much different. It only matters what you have, when you want to do something with them.