Our locks had electronic components, the Brit's didn't. Knowing what we do about the British and electical systems, it sounds like the Brit's wanted to be able to use their nukes if necessary. ;)
Cheers
The reason for this apparent lack of security is obvious. The British felt no need for additional security, given that the electrical system in the bomb was built by Lucas, making the bomb impervious to detonation, deliberate, accidental, or otherwise.