Business organisations have been responding as Britain prepares to leave the EU at 11pm today (Friday, January 31).
On Saturday, an 11-month transition period begins. The UK will remain the single market and the customs union until December 31.
The withdrawal agreement – which carries sanctions for what the EU called "backsliding or half measures" – will be a legally binding international treaty.
Little is known about what will happen next. Parliamentary scrutiny of Brexit has been restricted. Boris Johnson has not revealed his wishes or red lines, but most business organisations are calling for a tariff-free, quota-free deal.
Dr Adam Marshall, director general of the British Chambers of Commerce, said: "In our business communities, this historic moment will bring a mixture of regret for some and celebration for others – but this is just the end of the beginning, not the beginning of the end.
“Decisions made during the next phase of negotiations will influence the business environment for decades to come. Businesses are likely to face significant changes in the way they trade, both in Europe and across the world.
"The government must clearly communicate what those changes will be – and provide timely guidance and support to help firms adapt and make the most of new opportunities as Britain sets its own trading policies.
“Our business communities are pragmatic and want to move on from the emotional arguments around Brexit that have stymied confidence and investment for so long.
"They want to work with ministers to get the details right on issues like customs, regulation and immigration – and they are desperate to avoid more of the cliff-edges that have affected their operations in recent years.
“On the domestic front, spades in the ground for new infrastructure, better skills and training, and action to lower the up-front costs facing UK businesses are urgently needed to boost confidence and unlock investment.”
The Confederation of British Industry said it was time to focus on the future and build a new relationship with Europe.
Carolyn Fairbairn, CBI Director-General, said: “Today the UK leaves the EU, but our future prosperity remains connected. Despite the challenges of the last three years, together we have made progress. No deal has been avoided and a year of status quo gives time to shape that new relationship.
“Now the real work begins. It’s time to focus on the future and build a new relationship with Europe. This can reflect our shared values and mutual interest, and support bold global trade ambitions.”
Meanwhile, the Institute of Directors has said business needs time to prepare for a new relationship with the EU by the end of the year.
A survey of 950 firms conducted by the IoD found that directors are holding back on investment in business because of the continued uncertainty over Brexit.
Fifty-five percent of those polled said that they can only make planning and investment decisions with certainty once they understand what the relationship between the UK and the EU will look like. Just 35 percent of businesses feel the current withdrawal deal gives enough certainty.
“To give businesses any chance of being ready for the new relationship by the end of 2020, the government needs to be as clear as possible about what its intended destination is,” Allie Renison, the IoD’s head of Europe and trade policy, said.
"The Withdrawal Agreement provides clarity for the next 12 months and no further – enough for some organisations but not for those trying to take long-term decisions.
“With directors clear that negotiations with the EU are the priority right now, clarity is crucial for so many companies.”