Sir Roger Carr, chairman of British Gas owners Centrica, told Richard Edgar that David Cameron's "positive tone" on Europe was welcomed by the business community but that the prospect of a referendum means a "period of uncertainty."
He said businesses and politicians must prove that there is a "real, positive purpose in being in Europe that is good for the United Kingdom."
He added that Europe is "the largest single market we have" and "for us, it is about 50 percent of our exports."
"That kind of access, unfettered, is critically important to the long term while we build up other markets in parallel."
To the surprise of many Lib Dems, Nick Clegg appears to have played down the importance of the Coalition's divide on an in-out referendum.
Business leaders in Davos are worried about the Prime Minister's pledge to put Britain's membership of the European Union to a referendum.
With some in France keen to "roll out the red carpet" for a British exit, Germans favouring decentralisation welcome EU renegotiation talks.