I don't think it's Brexit. I think it's Tesco. Shopping with them has been a craps shoot for me from the start.
No, right now it's not Brexit. Right now it is some idiot who pulled my groceries order at Tesco. (sigh) I've placed another order, for a LOT of chicken. As of like 5 packs of 1.5 kilos. Because I'm going to fire that canner up bigtime. Made a note that substitutions were fine as long as it was chickenbreast. Didn't care about the brand, or if it was pre-cut. Just send the darned chicken!
Brexit shortages will come later. So I would assume that as supplies of things like olive oil and spanish onions run low, there will be times when I order that kind of thing that I don't get it.