The surprising result came in a poll of 2,500 "senior decision makers" by the FTI consulting firm, which underlined that business leaders could be overly complacent to the dangers of Britain's divorce from the European Union.
"We see fluctuations between countries and sectors but on the whole this is a surprisingly upbeat response," said John Maloney, head of FTI Consulting's Brexit taskforce.
The survey noted widespread optimism amongst the recipients, with a majority of companies confident that UK's future relationship with the EU will maintain principles such as the free movement of people and oversight by the EU's European Court of Justice.
The survey said that businesses are making light of current tensions, with the EU and Britain at loggerheads over the terms of a transition period after Brexit and big unknowns on future relations.
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"The results hint at a misreading of the political reality," said FTI's Hans Heck, a former Dutch diplomat.
There is "little prospect of companies getting comfort on the future trade agreement any time soon," he said.
Among the respondents, a big split existed on the fate of Britain's access to the EU financial sector.