British business leaders on Saturday urged the government to rule out a hard break with the European Union, saying the uncertainty over the terms of Brexit was impacting investment decisions.

"What we would like is the ruling out of the really worst options," Carolyn Fairbairn, the director general of CBI, Britain's biggest business lobby group, told BBC radio.

She outlined her case in an open letter to the government which was also signed by the heads of the EEF manufacturers' association, the International Chamber of Commerce UK and the techUK technology industry body.

They warned against a situation where Britain leaves the EU single market without having a new trade deal in place, meaning it would revert to trading under World Trade Organization rules.

"Falling into WTO rules in only 29 months from now, which is the prospective timetable, would mean up to 90 percent of goods could potentially have tariffs on them," Fairbairn said.

She said ruling out "some of these really negative options would "help to reassure investors that the UK was still a really good place to invest".