The whole 'buy British' means piss all if that means things cost more. I bet the vast majority of people who chose to 'buy British' are also in a position to be able to afford it. In reality, most people don't care where things are produced as long as they're cheap. 'Buying British' was also not a strong part of Brexit when there was lots of talk about getting potentially cheaper imports from other countries with different trade deals (take Mogg's promotion of Australian beef, for example).
Thinking about agriculture, there aren't enough workers out there to harvest crops. We've been heavily reliant on migrant workers as they've been prepared to work for the wages on offer. Wages will need to rise if we're to attract British workers to these places, where many are not a reasonable commute away. That'll result in food costs rising. I'm interested to find out if wages of lorry drivers has gone up as demand has far exceeded supply. That'll also result in costs rising.
Meanwhile, those on minimum wage jobs and low incomes will suffer the most.