The car park operator argues that by leaving the car park, they have explicitly agreed to the T&C's. The question would be whether that agreement is absolute and final, or whether there is a reasonable window where they could change their mind? Probably 90 secs elapsed between them leaving car park and re-entering car park.
They have said that the signage was relatively poor. A poster in the shop window, about A4 sized. No signs on entering car park.
Car park is very small though, 3 bays in front of the shop. You drive straight into the bays from the street. Not sure of the rules around signage and whether this would be grounds for appeal.