Business groups from across the EU have warned Theresa May on the threat to investment and jobs without "urgent progress" in Brexit talks within the next two weeks.
The delegation visited Downing Street to voice fears that current uncertainty over the UK's future trading relationship with the EU was damaging to firms across the continent.
Business groups from countries including Germany, France and Ireland joined UK counterparts in urging both sides in thge break-up to heed their united stance on the need for trade talks to be given the green light by EU leaders at their December summit in two weeks' time.
The EU's chief negotiator, Michel Barnier, declared on Friday that only "real and sincere progress" on the sticking points of citizens' rights, the Irish border and exit bill would be enough to recommend the start of the next phase of negotiations.
Emma Marcegaglia, president of the lobbying group BusinessEurope, said after meeting the PM: "We don't want uncertainty, we are very concerned.
"We know that if companies don't see certainty probably they will have a contingency plan and probably they will leave the UK, or they will invest less.
"So, these two weeks are extremely important."
The CBI's director-general, Carolyn Fairbairn, called or "urgent progress" saying the current lack of clarity meant that some firms were already beginning implement contingency plans in case of a hard Brexit.
She said: "With UK-EU trade worth more than €600bn (£534bn) each year, business groups from across Europe used today's meeting with the Prime Minister as a welcome opportunity to highlight the mutual importance of seeing real progress before Christmas.
"All business organisations present reiterated the damage a 'no-deal' scenario would do to trade.
"A transition period reflecting the current arrangements remains the priority on both sides of the Channel.
"While businesses welcomed the Prime Minister's Florence speech, we now need to move beyond warm words if jobs, investment and living standards are to be protected."
A Downing St spokesperson said of the discussions: "The Prime Minister reassured the group that Brexit meant the UK was leaving the EU, not Europe and reiterated her ambition for free and frictionless trade with the EU27 once the UK departs.
"She also expressed her commitment to giving businesses the certainty they need by agreeing a time-limited implementation period as soon as possible."