LONDON — The British government must quickly come up with a plan for post-Brexit trade relations with the European Union or risk a hit to investment and jobs, a leading business group said Wednesday.

In a letter to Prime Minister Theresa May, the British Chambers of Commerce said businesses’ “patience is wearing thin” with government divisions.

It said a lack of clarity meant businesses were starting to activate Brexit contingency plans, which could mean moving jobs from Britain to the EU.

Chambers of Commerce director-general Adam Marshall and president Francis Martin told May “there is no room for continued ambiguity as companies make investment and hiring decisions.”

“The government must set out its plans,” they said.

Britain is due to leave the bloc in March 2019, but the U.K. government remains divided over how close a relationship it wants to keep with the EU.

Britain says it wants a comprehensive free trade agreement with the EU, while still having the opportunity to make deals across the rest of the world. In practice, it will have to choose which one it wants more.

May’s Cabinet is split between supporters of a clean break and those who want to stick close to the bloc’s tariff-free single market and customs union.

A “war Cabinet” of key ministers is meeting Wednesday and Thursday to try to strike a common position.

British and EU negotiators are meeting in Brussels this week to try to agree details of a transition period that would keep Britain inside the EU’s single market, and bound by the bloc’s rules, for about two years after Brexit.

Britain wants the period to give businesses time to prepare for life outside the bloc. But pro-Brexit politicians in Britain have been annoyed by a passage in the EU’s proposals saying the bloc can “suspend certain benefits” of single-market membership if Britain breaks the rules.