I don't want to get all Orville and Keith Harris on you but you started your post with 'It can't', it can. For a European company using the UK as a manufacturing base, if the cost of imported materials is less than other costs, then a fall in the pound (which you have hinted at in your second paragraph) has the potential to lower your overall production costs (in Euro). Therefore, the question becomes, do those cost reductions outweigh the cost of any tariffs imposed? If they did, would a decision to relocate production to Europe be an economic one?
One other pedant point from your post, is the statement that WTO rules require tariffs, a 'fact' doubled down on in listing them as a reason for increased food prices. The WTO does not 'require' tariffs, only the even application of tariffs, should a member choose to impose them.