Law of Sale of goods

John agreed to sell 200 packets of organic flour to Anna. Anna gave a cheque to John for the full price of the flour and took delivery of 50 packets of the flour. They agreed that the remaining 150 packets of flour would be delivered after the cheque had been cleared. The cheque was dishonoured, and John decided not to deliver the remaining 150 sacks of flour. John also wished to take back the 50 packets of flour delivered to Anna.

Advise John on whether he could do so. (10m)