British nukes were protected by bicycle locks

To arm the weapons you just open a panel held by two captive screws - like a battery cover on a radio - using a thumbnail or a coin.

Inside are the arming switch and a series of dials which you can turn with an Allen key to select high yield or low yield, air burst or groundburst and other parameters.

The Bomb is actually armed by inserting a bicycle lock key into the arming switch and turning it through 90 degrees. There is no code which needs to be entered or dual key system to prevent a rogue individual from arming the Bomb.