Almost one in four small businesses are yet to review the potential impact of leaving the European Union on their suppliers or customers in the latest sign that many companies are not heeding government advice to “get ready for Brexit”.

The level of preparedness among employers with fewer than 50 staff is in stark contrast to that for companies with more than 250 workers. Fewer than 1 in 20 of these larger businesses are still to check whether their suppliers and customers are preparing for Brexit, according to research from R3, the insolvency trade body.

The group’s poll of 1,200 senior decision-makers in companies large and small found that, in total, about one in six had not reviewed their trading partners as the scheduled departure date of October 31 approaches.

Of those that had, one in three said they were worried by what they discovered while 40 per cent said they were reassured by their findings.

Duncan Swift, president of R3, said: “It’s a serious worry that a third of UK businesses feel they are exposed to a supply chain risk. It’s all very well making sure your own business has put adaptation plans in place, but these plans might not help if the businesses you depend on — customers and suppliers — are unprepared.”

The government has spent £100 million on a public information campaign to encourage businesses and consumers to get ready for the possibility of a no-deal Brexit.

The Federation of Small Businesses has warned that “many small firms have either not prepared or are finding that they can’t prepare”. Today it is calling on the Department for International Trade and the Treasury to issue “export vouchers” to fund research on new markets after Brexit.

Vouchers up to the value of £3,000 would help small companies on a range of costs, from translation services to additional market research and finding new clients through overseas trade fairs, the employers’ group said.

Mike Cherry, the FSB’s national chairman, said: “Small businesses are being made to wait for the updated publication of the government’s revised UK tariff schedule that would apply in the event of a no-deal Brexit scenario, which must be published as a matter of urgency. The continued uncertainty is harming small firms’ ability to plan.”