Video report by ITV News Political Correspondent Libby Wiener
CBI Director General Tony Danker has told ITV News businesses are in the dark about how to implement the post-Brexit trade deal properly once the transition period ends.
Among the issues are firms having "no idea" how Europe will police its borders from, the boss of the Confederation of British Industry warned.
Mr Danker urged the government to put pressure on the EU to provide clarity on the borders issue, and told ministers they must turn the more than 1,200 page 'Trade and Co-Operation Agreement' into "practical guidance" for firms.
Mr Danker said: "Up until Christmas, most businesses in the country had done all they possibly could do to prepare for whatever the eventuality was.
"But then on Christmas Day we had 1,200 pages of legal text come down the chimney and I have to tell you, it really changes the nature of our trading relationship with the EU.
"So at this stage, with three days to go, we urgently need that legal text turned into practical guidance."
The warning comes as all 28 EU ambassadors gave provisional approval for the deal.
A spokesman for the German EU presidency said the ambassadors had unanimously agreed to “green light” the settlement hammered out on Christmas Eve.
So what is and isn't in the deal?
Boris Johnson said the deal covers trade worth around £660 billion and that it is a "good deal for the whole of Europe", which means:
Goods and components can be sold without tariffs and quotas in the EU market.
It will allow the share of fish in British waters that the UK can catch to rise from around half now to two-thirds by the end of the five-and-a-half year transition.
Allegations of unfair competition will be judged by an independent third-party arbitration panel with the possibility of a “proportionate” response.
The Erasmus student exchange programme will be replaced in the UK by a worldwide scheme named after code breaker Alan Turing.
However, on financial services, a vitally important sector to the UK, Mr Johnson conceded he had not got all he wanted.
Cabinet Office Minister Michael Gove warned time was “very short” as he acknowledged there were likely to be some “bumpy moments” as the new arrangements came into effect.
"I think lots of businesses are ready, particularly the larger businesses, some smaller businesses will still want to do a bit more in order to be ready," he told BBC Breakfast.
"We are there to help them and the advice that we’re giving, and also the money that we’ve invested in making sure that people can be ready for customs procedures, is designed to help.
"I’m sure there will be bumpy moments but we are there in order to try to do everything we can to smooth the path."