Technically, while the Sea King had been retired from UK military service some years ago.....there was still two that remained airworthy and flying since then on the military register, and a third was later brought back to airworthy. These 3 could be seen on a regular basis flying during the past 5 or so years around the south coast, being operated by HeliOps in Portland who have been operating 3 x ex-RN Mk.5's on the military register under a contract to train GermanMarineflieger SAR aircrews for a good few years, who still operate the Sea King and that contract ended a short while ago, but they were then contracted by UK Govt to train Ukraine crews as a follow-on, and its these 3 x airworthy Sea Kings that are being donated to Ukraine. They were already airworthy and flying, they weren't made airworthy just for Ukraine.
HeliOps have a huge hangar full of Sea-Kings and pretty much the entire store of ex-MOD parts supply for them.