Surely a contract has been entered into at the point payment is taken?
I think their T&Cs reasonably well cover that a contract isn’t established at point of payment, or order confirmation, but at shipping confirmation.
2.3 Acceptance of your order and the formation of a contract between us will take place when we send you an email confirming that the products you have ordered are being shipped to you, unless we have notified you that we do not accept your order or you have already cancelled it.
… but, I think you could reasonably argue that their email stating that “shipment will be delayed” constitutes confirmation that the products ordered are being shipped to you. If not, the email would just have stated “order processing is delayed”, surely?