LONDON (AP) — A major British business group warned Tuesday that companies need answers over Britain's post-Brexit relations with the European Union, as British Prime Minister Theresa May tried to unite her feuding government around a common vision for future trade with the bloc.

The British Chambers of Commerce said — two years after U.K. voter chose to leave the EU — firms still don't know what arrangements will be in a host of areas including tariffs, tax, customs and aviation.

Director-general Adam Marshall said "business patience is reaching a breaking point."

The Chambers of Commerce said Brexit uncertainty was causing a "significant slowdown" in business investment in the country, with many firms making contingency plans to move their money elsewhere.

Major manufacturers including aviation giant Airbus — which employs 14,000 people in Britain — have warned they will leave Britain if there is a "no deal" Brexit, that is if the EU and the U.K. cannot agree on their future trade relations before the U.K. leaves the bloc next March.

Some members of the U.K. government have downplayed the corporate warnings. Pro-Brexit Foreign Secretary Boris Johnson is reported to have dismissed business concerns with a four-letter expletive.

But Marshall said "businesses have every right to speak out when it is abundantly clear that the practical questions affecting the competitiveness of their firms and the livelihoods of millions of people remain unanswered."

Britain is due to leave the 28-nation bloc in March, and the EU has warned that May's government must provide realistic proposals soon or risk crashing out without a deal.

May will gather her fractious Conservative cabinet on Friday to try to hammer out a plan for customs and trade ties. She is caught between pro-EU lawmakers who want to retain close economic ties with the bloc and its market of 500 million people and pro-Brexit lawmakers who want a clean break to make it possible to strike new trade deals around the world.

Pro-Brexit Conservative lawmakers have warned May she could be toppled by her own party if she opts for a compromise Brexit that keeps Britain closely aligned to EU rules.

But former Foreign Secretary William Hague urged the Brexiteers to pipe down and unite behind May.

"Everyone threatening Theresa May with chaos, revolt, resignations, and a leadership election if she doesn't do as they wish needs to think carefully about what might be the consequences of their actions," he wrote in the Daily Telegraph.

He said "the choice is either to back a compromise plan now or to end up with a more watered-down version of Brexit that would be forced on ministers anyway" by Parliament.