First came the Brexit trade deal. Now comes the red tape.

Four days after sealing a free-trade agreement with the European Union, the British government has warned businesses to get ready for disruptions and “bumpy moments” when the new rules take effect on Thursday night.

Firms are scrambling to digest the details and implications of the 1,240-page deal agreed on Christmas Eve, just a week before the year-end deadline.

Ambassadors from the 27 EU nations, meanwhile, gave their unanimous approval to the deal on Monday.

“Green light,” German spokesman Sebastian Fischer, whose country currently holds the EU presidency, said.

The approval had been expected, since all EU leaders have warmly welcomed the deal, which is designed to put post-Brexit relations between the EU and Britain on a reliable footing.

The agreement needs formal approval from Britain’s Parliament, which is scheduled to vote on it on Wednesday, and from the EU’s legislature.

The UK left the EU almost a year ago, but remained within the bloc’s economic embrace during a transition period that ends at midnight Brussels time on December 31.

The agreement, hammered out after more than nine months of negotiation, will ensure Britain and the 27-nation EU can continue to trade in goods without tariffs or quotas.

“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,” Michael Gove, the British Cabinet minister in charge of Brexit preparations, told the BBC.

British Prime Minister Boris Johnson’s Conservative government argues that any short-term disruption from Brexit will be worth it, because the UK will now be free to set its own rules and strike new trade deals around the world.

Despite the deal, uncertainty hangs over large chunks of the relationship.

The agreement covers trade in goods, but leaves the UK’s huge financial services sector uncertain how easily it can do business with Europe after January 1.

The British territory of Gibraltar, which sees thousands of workers cross over daily from Spain, is also in limbo since it was not included in the deal.

And the deal has angered one sector that the UK government vowed to protect: fishing. The economically minor but hugely symbolic issue of fishing rights was a sticking point in negotiations, with maritime EU nations seeking to retain access to UK waters, and Britain insisting it must control its seas.

Under the deal, the EU will give up a quarter of the quota it catches in UK waters, far less than the 80 per cent Britain initially demanded. The system will be phased in over five-and-a-half years, after which the quotas will be reassessed.

“I am angry, disappointed and betrayed,” Andrew Locker, chairman of Britain’s National Federation of Fishermen’s Organisations, said.

“Boris Johnson promised us the rights to all the fish that swim in our exclusive economic zone and we have got a fraction of that.”