Thank you both! I was aware of a 'get out of jail' process with this, but as I was at the shopping centre, easiest solution was to go an obtain a new battery.
I did feel uneasy leaving it unlocked (even for a few minutes), so I didn't hang about.
I do recall hovering the key around the area where the normal ignition key goes, but nothing seemed to work, maybe I was just not patient enough with it!
Having a spare battery to hand is a good move!