Possibly WM.
It will not be comfortable for anyone.
Then again it would be nice to know what the median and best cases were. Of course nobody is going to leak those, they might sound too good.
On the other hand, leaking a worst case scenario has its uses. When it is not that bad, people will be relieved. If you leak the best case everyone will be disappointed when we don't make it.
Looking at the list, this is a list of "do nothing and fail". For instance, reading this, you would assume the EU is the only country which produces food in the world. Or that we don't have shipping ports and can only get food via trucks from the EU.
With the correct government planning it is quite feasible for 50% of our food to arrive, Jan 1st, via ship, from the rest of the world. It could even be tariff free if we chose as we will be in command of that. Net effect? Food prices go down.
But without a disaster document like this, the plans will never be executed.
As for food production and competitiveness, it is worth reading a
Dutch article on EU agricultural. Competitiveness.After that, you can go and find one on the difference between US agricultural tarrifs and the EU regime.
When we leave, without EU tariffs being applied, the whole world is going to want to sell food to the UK. It is also going to be cheaper than the UK. Our citizens are used to paying EU prices. Unless we start issuing EU level tarrifs, we are going to be exposed to very low food prices.
EU tariffs on US milk are close to 90%. If we do not apply the same, our entire milk imports from France could switch to the US in a month, lowering our prices and crippling France.
But, in order to do this, we need a worst case.