If you've made 'a reasonable attempt to pay' then it won't stand up.
So no, if you are given more change than you should have, and leave, then it's basically tough luck for the shop.
I know as my mate used to be a petrol station manager... If someone fills up the car, then goes into the shop, picks up a bag of crisps or whatever.. Goes to the counter and they just charge them for the packet of crisps and leaves... The police aren't interested as the CCTV shows you walking in and swiping your card at the counter... So there is pretty much no way to prove that you acted dishonesty.
So no, if you are given more change than you should have, and leave, then it's basically tough luck for the shop.
I know as my mate used to be a petrol station manager... If someone fills up the car, then goes into the shop, picks up a bag of crisps or whatever.. Goes to the counter and they just charge them for the packet of crisps and leaves... The police aren't interested as the CCTV shows you walking in and swiping your card at the counter... So there is pretty much no way to prove that you acted dishonesty.