I think you may have misread -I didnt suggest it was the only cause.
have a look at the impact of the additional brexit red tape:
sanitary and phytosanitary controls
customs declaration
transit documents
here is a simple example:
a fruit and vegetable wholesaler buys mushrooms from Poland 3 times a week
he has to use a customs agent now to sort out all the documentation
and because of the customs checks it takes an extra 24 hours in transit -that reduces the freshness of the mushrooms and increases wastage
hauliers have ramped up prices for the journey across the Calais Dover route because the delays cost a fortune, not to mention long delays means fresh goods go off faster
did you know as an EU member the UK had fully integrated supply chains across Europe, any British business could import seamlessly
and now there are massive problems with non tariff barriers