The poll of FTSE 350 firms – the largest 350 listed on the London Stock Exchange – was conducted by Icsa, which advises companies on corporate governance. Confidence was at its lowest since surveys began in 2012, said Icsa, and dramatically down since May, before the EU referendum.

But firms did not see Britain leaving the European Union as the main risk they faced. While 59 per cent see Brexit as potentially damaging, just 43 per cent regard it as a “principal risk”.

Cyber security was seen as a primary and increasing danger by four out of five firms, the poll revealed. But companies had downgraded “political risk” – including Brexit – to their joint lowest concern.

However, Peter Swabey of Icsa said: “It remains to be seen how sentiment will change the closer we get to triggering Article 50.”

In what was seen as a further sign of confidence in Brexit Britain, online fashion retailer ASOS has announced it will hire an extra 1,500 workers over the next three years to join the 2,500 it now employs at its north London base.

Chloe Westley, of the Change Britain group campaigning to make a success of Brexit, said: “This commitment to the UK by some of our largest employers is another vote of confidence in our economy and is good news for workers.

“Major companies like Google and Apple have announced plans to invest billions of pounds and create thousands of jobs in the UK. It’s clear we’re open for business.”

The Government will seek the “best deal” when Britain leaves the EU, Brexit Secretary David Davis said yesterday.

He chaired a meeting in London with bosses from several car manufacturers, including Nissan which recently said it would go ahead with two new models at its Sunderland plant. Companies at the meeting also included Jaguar Land Rover, Ford and Vauxhall.

Mr Davis said: “Our automotive sector is one of the most productive in the world and we want to see it go from strength to strength.”

The UK car industry employs 800,000 people and produced 1.5 million cars last year, with 80 per cent being exported.