I think it is probably worse than even the good politician states. The reason is that many of our food producers rely on imported cereals and stuff like soya beans/meal to feed their animals. Similarly, most of the fertilizer used to boost production is imported. This probably increases the overall level of demand to over 70%.
In modern times, it was always so.
In both the 1st and 2nd world wars, the lack of imported food led to big problems.
Protein is a major problem as it takes a lot of green stuff to produce a bit of meat/fish/eggs/dairy stuff. If we all went vegetarian or at least cut down of the amount of meat etc, it would be a lot better - and so would we!
In medieval times, the ordinary peasant was lucky to eat meat once a week so there is a precedent for this.
We could produce food artificially. Back in the 70's, both BP and Shell developed techniques for producing protein to make a meat substitute similar to Quorn (which is, I think, based on imported soya) using paraffin or natural gas. The process was quite efficient compared with traditional methods and a lot of countries were interested (like Norway, the Middle East) where meat production is difficult and expensive.
But the whole business was shut down. The process based on paraffin was stopped on the basis that there remained a small amount of paraffin in the product. The fact that most of the dried fruit we eat is coated with the same paraffin to stop the currents/raisins/sultanas sticking together is neither here or there. The natural gas approach went a similar way.
The technology is still there so it would be possible to revive it. Other than that, I don't see what can be done.