The tweet below is rubbish.
The UK has a free trade agreement with the EU. So no Brexit import tariffs.
British food is not shrinking although the government could stop paying farmers to grow wildflowers if this becomes a real problem.
Who will feed us? Australia, New Zealand, Canada, South Africa, Kenya, Morocco, Egypt, Turkey, Brazil, Argentina, Chile, Peru, Colombia, Mexico, Vietnam, Malaysia, Uruguay, Costa Rica, Ghana, etc etc...