brexitcentral.com/erg-publish-ri…
Couple of issues here. Big ones.
This is meant to buy time to negotiate something for the future.
That's simply not how that works. Most trade negotiations begin based on the text/approach of a previous agreement as the "model."
They still take years.
Step 1. UK crashes out of the EU at the end of March, with all the massive disruption that entails.
Step 2. Businesses adjust, many failing or spending tens of thousands.
Step 3. UK and EU begin negotiations on an FTA based on Canada.
Step 5. The FTA is signed and implemented.
Step 6. Businesses adjust AGAIN, undoing all or part of the measures they took in Step 2.
It's jumping off the cliff edge and hoping you can fly because you've seen a bird do it.
/End
P.S Good analysis of the ERG paper by @DavidHenigUK if you want detail.