When George Martin steals the battledress, he manages to put it on whilst still handcuffed to Willie Stannard......... Stannard is seen cutting the seam of the jacket Martin is wearing, and removing it, then Martin tells Stannard to help him on with the battledress and 'out with the needle' and Stannard is seen sewing the sleeve back up.
It is never explained exactly how Jack Warner managed to extricate himself from his half of the handcuffs, because they appear to have been sprung rather than sawn off...... In the scenes where Martin (Jack Warner) is sawing at the handcuffs, he is always sawing the part of the handcuff around his wrist, deliberately done so Stannard is left with the cuffs. However, when they are separated and Stannard holds up his arm with the handcuffs attached, it does look as if the handcuffs have been sprung rather than sawn.