Bad tasting expired kips

I have purchased one of my beloved snacks the spring onion kips biscuits yesterday from the savemor in Vivo. I opened it today and had a bite. What an appaling taste. Like sour dough. Had one more with same effect. Decided to check the expiry date and the BB date is December 21😱 How can retailers be allowed to sell items that have expired two months ago. I don't know if I will ever be able to eat kips again. I will be sharing this everywhere. I am very dissapointed.