Self-Sufficiency in the UK

I heard this on Radio 4 (can't remember which programme it was):

55% of farmland in the UK is used to grow feed for farmed animals, a highly inefficient way of producing food. If we were plant-based, the UK could be self-sufficient for food.

According to Global Food Security UK:

The UK is not self-sufficient in food production; it imports 48% of the total food consumed and the proportion is rising. Therefore, as a food-trading nation, the UK relies on both imports and a thriving agricultural sector to feed itself and drive economic growth. [UK Threat - Food Security UK 10/Mar/2017]

The Vegan Society cites a Harvard Research paper: "Eating Away at Climate Change with Negative Emissions":

UK can sustain itself if it converted all animal farmland to forest, Harvard research shows [Vegan Society Blog 19/Apr/2019]

The Vegan Organic Network uses higher figures for the amount of land used to farm animals:

85% of land needed to produce UK food supply is used for animal products [Vegan Organic Network news 10/May/2019]

Even the pro-animal agriculture BBC Countryfile television programme posts an opinion that meat production is preventing the UK from being self-sufficient for food, quoting Prof Tim Lang to answer the question: Can the UK feed itself?:

“Yes, but it depends on what we eat,” says Professor Tim Lang. “We’ll have to cut eating meat down to once a week. We have to rebuild our horticulture and put more money into primary food production. There has to be a shift in how we grow our food.” [Country File: Can the UK feed itself after Brexit? 05/Jan/2018]

The problem is that using animals for food is extremely inefficient:

The use of arable land to feed farmed animals is very inefficient. ... Though chickens are the best converters of plant-to-animal-protein of all the main animals reared for their flesh, about 78% of all the plant protein that was fed to a chicken in the USA about a decade ago was not converted to protein that is eaten by human beings. [Animal (De)liberation: Should the Consumption of Animal Products Be Banned? Decker J 2016]