The BBC has a report about the security of British nuclear bombs prior to 1998:
Newsnight has discovered that until the early days of the Blair government the RAF’s nuclear bombs were armed by turning a bicycle lock key. There was no other security on the Bomb itself. While American and Russian weapons were protected by tamper-proof combination locks which could only be released if the correct code was transmitted, Britain relied on a simpler technology
Papers at the National Archive show that as early as 1966 an attempt was made to impose PAL security on British nuclear weapons.
The Chief Scientific Adviser Solly Zuckerman formally advised the Defence Secretary Denis Healey that Britain needed to install Permissive Action Links on its nuclear weapons to keep them safe.
“The Government will need to be certain that any weapons deployed are under some form of ‘ironclad’ control”.
The Royal Navy argued that officers of the Royal Navy as the Senior Service could be trusted:
“It would be invidious to suggest… that Senior Service officers may, in difficult circumstances, act in defiance of their clear orders”.
Neither the Navy nor the RAF installed PAL protection on their nuclear weapons.
You can read the full article HERE.