Food inflation after Brexit

I have just seen Three Blokes in the Pub episode 15 and realised the effect a hard Brexit will have on pensioners (and anyone else who has an income uplift calculated on the basis of the CPI this autumn). Food costs, which are a major component of the spending of lower-income households, will go through the roof in spring 2019. Unless the border between the UK and the 27 is frictionless, the increased cost of imports because of increased insurance costs, expensive paperwork and delays at ports, coupled with the inevitable further fall in the value of sterling, will make 2008 look like a minor correction.