More clarity on the Brexit transition is needed to stop companies proceeding with contingency plans despite the progress announced on Friday, the CBI has warned.
Paul Drechsler, president of the business lobby group, said companies had begun triggering plans months ago.
However, more detail could help suspend further action by firms, he said.
Sterling was trading higher at just under $1.35 and €1.15 after the announcement in Brussels on Friday.
The CBI chief also called for “unconditionality” about the status of EU citizens living in the UK.
“It’s an important political milestone, but clarity on transition is the most important thing from a business point of view at this stage,” Mr Drechsler told BBC Radio 4’s Today programme.
The Institute of Directors echoed the CBI call for certainty on the rights of EU citizens.
Stephen Martin, IoD director-general, said companies urgently needed certainty about the future of EU staff in the UK.
“We have grounds to hope now that our members will be able to send their employees off for the Christmas break feeling more comfortable about their status here,” he said.
“We look forward to further clarity about what the UK’s objectives are for that new relationship, as well as a firm commitment on transition in the very near future.”
Adam Marshall, British Chambers of Commerce director-general, said “clarity and security” for European employees had been the biggest priority for UK companies since the referendum vote.
“We are delighted that they, as well as UK citizens living and working in the EU, now have more clarity and can plan their future with greater confidence,” he said.
As attention turns to trade negotiations, the BCC said companies wanted “absolute clarity” on the long-term deal being sought.
“Businesses want answers on what leaving the EU will mean for regulation, customs, hiring, standards, tariffs and taxes,” Mr Marshall said.
“The job of the UK government and the European Commission now is to provide those answers – and do everything in their power to ensure vibrant cross-border trade between the UK and EU countries can continue.”