Theresa May has been warned that business chiefs' patience over Brexit is "wearing thin" and Westminster must get to grips with the challenge.
British Chambers of Commerce (BCC) director general Adam Marshall said firms want clarity and results from the Government and suggested industry was dismayed by "division and disorganisation" across Westminster.
The BCC represents firms employing more than five million people across the country and Mr Marshall is the latest senior business figure to demand a clearer picture of what a Brexit deal will involve.
"Some very big decisions lie ahead," Mr Marshall told The Observer.
"Getting the twin challenges of Brexit and the economic fundamentals right will require leadership, consistency and clarity - after a year in which business has been dismayed by what it sees as division and disorganisation across Westminster."
He added: "Businesses have been very patient in waiting for clarity on Brexit in the 18 months since the referendum. That patience is now wearing thin. Businesses want answers, they want clarity and they want results."
The BCC, the Confederation of British Industry (CBI), Federation of Small Businesses (FSB), Institute of Directors (IoD) and EEF, which represents manufacturers, have all called for the terms of a transition period after the UK leaves the EU in March 2019 to be agreed as soon as possible, to give firms time to plan for the new relationship with Brussels.
The longer the process drags on, the less value a transitional deal will have as firms will already have been forced to implement contingency plans which could see them shift work and jobs to one of the 27 other European Union members.