(This April 17 story was refiled to add name of debate host)

FILE PHOTO: Frans Timmermans, the newly elected Party of European Socialists President, speaks during the Party of European Socialists annual meeting in Lisbon, Portugal, December 8, 2018. REUTERS/Pedro Nunes/File Photo

STRASBOURG, France (Reuters) - Britain should use the next few months to “cool down and rethink” its decision to leave the European Union, the socialist candidate to head the next European Commission, Frans Timmermans, said on Wednesday.

Last week EU leaders gave Britain an extension of its departure date until Oct. 31, with the possibility of leaving sooner if parliament ratifies a divorce deal Prime Minister Theresa May has negotiated with the EU. Lawmakers have already rejected the deal three times.

“I absolutely hope that the UK might stay in the EU,” Timmermans, now the Commission’s first vice president, said in a television debate on France 24 with his main rival, Manfred Weber of the centre-right European People’s Party (EPP).

“I hope this period of extension will be used for Britain to calm down and rethink things a bit, perhaps for politicians to be more responsible with the promises they make, and then look at the issue again later this year,” the Dutchman said.

“Who knows what might change in the meantime?” he said.

Timmermans was expressing a sentiment shared by some in the EU, notably the chairman of EU leaders, Donald Tusk, that Britain could still change its mind and stay in the EU.

LABOUR TO TIMMERMANS’ RESCUE?

Polls show that enough Britons may have had a change of heart about Brexit since the 2016 referendum, in which they voted to leave the bloc by 52 to 48 percent. But May and her government remain strongly opposed to holding another vote.

Timmermans hopes to replace the EPP’s Jean-Claude Juncker as head of the European Commission, the most powerful of EU institutions. He is running on a ticket from the EU’s second biggest political family, the socialists.

Britain is likely to still be a member of the EU at the time of the European Parliament elections on May 23-26, which means it would take part in the vote. Britain’s opposition Labour Party, which backs a second referendum, could help Timmermans’ socialists win more seats in the 751-seat European assembly.

Weber does not stand to benefit in the same way from British participation in the EU elections because no UK parties belong to the EPP, currently the largest grouping in the parliament.

“I have a problem that they (Britain) are now participating in the EU elections, are deciding about the future of our union,” Weber said during the TV debate with Timmermans.

“That is not easy to understand. I respect the outcome, and if they are part of the EU, they have the right to vote – don’t get me wrong,” he added.

The EU political family with most seats in the European Parliament expects its candidate for Commission president to land the job, although the decision formally lies with EU leaders.

Latest polls - which assume UK participation in the elections - show the EPP winning 178 seats and the socialists getting 144 seats.