The survey, conducted by international law firm Gowling WLG, also found that two-thirds of the 533 companies polled said the UK’s June 23 Brexit vote had already impacted on investment choices in Britain.
Those businesses most likely to relocate were in the food and beverage, life sciences and financial services sectors, while aerospace companies were the most likely to stay put, according to the survey.
The results come amid concerns that any UK government plans to take Britain out of the European single market will have a negative impact on trade and investment.
"The strong UK-US trade relationship that has been carefully nurtured over the past fifty years is in serious jeopardy," said Bernardine Adkins, Gowling WLG's head of EU, Trade and Competition.
EU's chief Brexit negotiator @MichelBarnier has told MEPs he is NOT against a transitional agreement, but would need clear end point— John Stevens (@johnestevens) November 30, 2016
"This is despite a wide consensus amongst US firms that the unique dynamics of the UK market and its access to the rest of the EU drive their preference for doing business here. Concerns that Brexit will have an effect on current investment decisions mean this needs addressing now, not later."
Fears of Job Losses, Legal Delays
The findings come after a report from the House of Lords concluded that a failure to strike a transitional Brexit deal could result in the loss of tens of thousands of banking jobs in the UK, as rival European capital look to lure London's lucrative banking industry.
The government, under Conservative Prime Minister Theresa May, is under pressure to publish a plan setting out the country's objectives during EU divorce talks, with some opposition politicians calling for MPs to be given a final vote on any Brexit deal negotiated between the UK and the EU.
Corbyn asks where PM's Brexit plan is? Says uncertainty over N Irish border, financial firms are "quivering over relocate button"— Faisal Islam (@faisalislam) October 26, 2016
May's rhetoric on immigration has led to predictions the UK will leave the European single market, with the prime minister pledging to trigger Article 50 by the end of March 2017.
However, the government could face a parliamentary backlash against its Brexit timetable, with a High Court decision ruling that MPs must vote on legislation before kicking off the official divorce process.
The government has appealed the decision in the Supreme Court, with a final decision expected within a couple of weeks.