Lockable shopping trolley

This trolley has a divider, which folds out to create a compartment into which shoppers may place their shopping bags. The compartment may only be locked on entry to the store (or secured area) and unlocked on exit, using a key secured to the wall. This would save the store requesting intrusive searches, and me spending five minutes at the checkout explaining why I'm refusing. The lock need only be simple and inexpensive, as tampering attempts would have high visibility.