Snap opinion polls at the conference of the Guild of Travel Management Companies (GTMC) suggest a remarkable swing in opinion on the EU referendum.

A vote on the first day of the GTMC conference in Marco Island, Florida, found 63% support among corporate travel executives and suppliers for Britain to remain in the EU. Just 12% were in favour of Brexit and 15% undecided.

But a repeat of the poll a day later following speeches by Brexit-supporting economist Gerard Lyons and The Times political commentator Tim Montgomerie recorded 44% in favour of Brexit and 41% for remain.

The astonishing turnaround came after Montgomerie told the conference: “I think people will choose the status quo. But I believe it would be better to go through a painful transition for two years.

“The EU is dysfunctional. It’s losing its share of world trade twice as fast as the US. Europe is sinking. The levels of unemployment, the levels of austerity, no growth – it needs a shock.

“Europe is working for the haves, for people who have second homes in Spain. But for lots of people life is tough.”

He argued “Brexit would be good for Britain, but it would be good for the EU as well.

“The EU will have to go through massive soul searching if the world’s fifth largest economy leaves. The level of austerity the EU is imposing on the periphery of Europe is socially unacceptable.”

Abta head of public affairs Stephen D’Alfonso disagreed, telling the conference: “The shock is potentially unsustainable for many businesses. Can businesses hold on for two years of uncertainty about travel?”

When Abta consulted its members, D’Alfonso said: “We found very few had a view other than that the risks of leaving were great.”

He insisted: “From a travel perspective, there is a strong case for remain.”

Montgomerie said the divisions in the Conservative Party over the vote would be hard to heal. He told the conference: “It’s a huge mess and it will not be easy for people to sit down together afterwards.

“If it is a 15-point defeat for Brexit that is one thing. If it’s four or five points, the Leave campaign will feel cheated. Unless there is an emphatic result it will be poisonous for some time to come.

“There will be a hangover. Tory MPs and ministers are openly attacking the prime minister. It’s an extraordinarily unhappy party. Don’t underestimate the seriousness of the political environment we are in.”