Yes, possibly thermal expansion and no provision to accomodate the movement. Was the sun shining on the door at the time?
A former workplace had a wall of glass blocks under the windows in the stairwells. On summer afternoons, the sun would shine on the wall and the glass blocks would occasionally explode. This was rather unsettling, if you were passing through the door some floors below.
A new door might have the same problem. The door is defective and Wickes should pay for it and the cost of planing to size, hanging and completely finishing it, or the costs of repair, if less. If their supplier is at fault, then they recover their costs from the supplier with whom they have a contract.