Where to hide a naval base in the British Isles

What is the best part of the British Isles for a secret naval base?

Anglesey is the preferred answer because of its sheltered strategic position and infrastructure, with Skye as an alternative.

Anglesey is the preferred location because of its Irish Sea position, the approach around Britain, and its infrastructure links. Skye is another suggestion, although a joke about political publicity casts doubt on keeping it secret. Felixstowe could conceal activity among normal port operations, but passing shipping would also give observers cover and make surveillance harder to identify. Portsmouth offers the possibility of hiding inside an existing naval base. Its many ship-watchers would be likely to notice activity that did not fit the normal pattern.