Nearly two-thirds of businesses have yet to do any risk assessment of a no-deal outcome in the Brexit negotiations as “Brexit fatigue” sets in, the British Chambers of Commerce has found.

With six months to go until the UK leaves the EU, the BCC said many small- and medium-sized businesses (SMEs) were “either awaiting more clarity before they act or are suffering from Brexit fatigue and have switched off from the process because they don’t believe they will be affected”.

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Adam Marshall, the director general of the BCC, said: “Too many businesses across the UK are still not ready for Brexit. Many smaller firms don’t have the capacity to scenario plan, don’t think they’ll be affected or have simply switched off from the process altogether.”

Facebook Twitter Pinterest Britain is scheduled to leave the EU on 29 March 2019. Photograph: Stefan Rousseau/PA

A survey for the BCC found that a quarter of companies that import or export would cut investment if there is no deal.

In findings that alarmed the BCC, 18% of respondents said they would cut recruitment and a fifth said they would move part or all of their business to the EU to ensure they could still export. The survey involved 2,500 firms across the UK between 1 August and 21 August.

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Edward Winterton, UK chief executive of Bibby Financial Services, which partnered with the BCC on the survey, said: “The consequences of a no-deal outcome could be disastrous for the 5.7m SMEs in the UK, particularly for those buying and selling goods within the EU.”

The BCC is now calling on the government to redouble its efforts to reach an agreement with the EU and launch a specific programme to help businesses prepare for change and prevent a slump in investment and recruitment.

Last week the Dutch prime minister said his country was more prepared than the UK for a no-deal Brexit, and the Irish government launched a national campaign of events and workshops to help businesses understand potential changes in export regimes.

Businesses that export to the EU will require a suite of changes in their operations, including knowledge of tariffs, rules of origin definitions and the demands of filling in 54 boxes of information for customs declarations forms required for each consignment.

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Exporters of food and agricultural products or animals will need to be informed that if there is no deal there will be an effective trade embargo in exporting to Europe because of a new layer of certification the EU will have to supply for a “third country”. The National Farmers Union has been told this could take six months.

The BCC said larger firms and those that were internationally active were the most exposed in a no-deal scenario. More than a quarter (28%) of firms with more than 50 employees and 24% of those that export or import internationally say they would cut investment plans.

The survey found that 69% of firms with fewer than 10 employees had not completed a risk assessment, compared with 24% of firms with more than 250 staff.

Marshall said: “With six months to go until the UK’s planned departure, firms still don’t have answers from government to the most basic questions about future trading conditions.”