I think the reporter probably jumped the gun, without being properly informed.

I suspect the bicycle locks is just one layer of security and that like others have said the bicycle locks probably only power up the bomb. There probably are additional levels of security, that hopefully require remote code activation. I suspect a lot of this information is classified and compartmentalized; so the reporter was probably only shown one level of security (a compartment).

It would be the equivalent of driving by a base that has nuclear weapons, and showing a reporter a chain-link fence, and the reporter assuming that the chain-link fence is the only defense, and that people can access nuclear bombs with only a set of wire cutters. Somehow I suspect our nuclear bombs are guarded by more than a chain-link fence, just as I suspect British nuclear bombs require more then a bicycle lock to fully arm them.

As others have said I suspect the bicycle lock is likely only a pre-arm, or power on.