(BBC) -- Companies have been left in the dark over planning for Brexit amid an "information void", a leading business group has warned.
The Institute of Directors has called on the government to speed up guidance on what companies should expect if no deal on leaving the EU is reached.
Its survey of 800 business leaders showed fewer than a third had made any Brexit contingency planning.
Many said they were waiting for clarity about the future EU relationship.
Almost half of respondents did not anticipate drawing up nor implementing any contingency plans for Brexit, with a similar number not expecting Brexit to affect their organisation.
Stephen Martin, director-general of the IoD, said it was difficult to blame companies that had failed to prepare for the UK's departure.
"When it comes to knowing what to plan for and when, firms have been left in the dark," he said.
"Trade associations like the IoD are doing their best to fill the information void, but the reality is that many companies feel they can only make changes once there is tangible information about what they are adjusting to.
"As long as no deal remains a possibility, it is essential that the government steps up to the plate and provides advice on preparing for such an outcome."
The IoD called on ministers to speed up publication of the technical notices on Brexit. Mr Martin said doing so would remind companies what they needed to do to prepare for all Brexit eventualities.
"Any transition period must take account of the fact that many businesses feel they can only adjust once there is clarity about the direction of travel."
The Institute of Directors is a non-party political organisation founded in 1903 and has about 30,000 members.
They include directors from all industries, as well as the public and voluntary sectors, and range from the bosses of small start-ups to chief executives.