Merlin's lockpick

Bedevere once mentioned that the version of Merlin with whom he was familiar possessed a magic lockpick that could open any door. (AUDIO: Broken Bonds)

Behind the scenes
There are many hints, throughout Bedevere's appearances in the P.R.O.B.E. series, that the version of Merlin he was familiar with was the same one whose shadow hangs over the Doctor Who television story Battlefield — namely, a far-future version of the Doctor. In this context, "Merlin's lockpick" which could open any door might be intended to be a sonic device, or even the Doctor's sonic screwdriver itself.