FILE PHOTO: Anti-Brexit demonstrators wave flags outside the Houses of Parliament, in London, Britain, September 10, 2018. REUTERS/Hannah McKay

LONDON (Reuters) - Britons would vote 52 to 48 percent in favor of remaining in the European Union were there to be another Brexit referendum, showing only a small change in public opinion since the 2016 vote, according to a poll of polls.

But researchers cautioned that a narrow victory for those hoping to reverse the decision taken two years ago would be heavily contingent on getting those who did not vote last time to turn out.

The figures are calculated by taking the average of the six most recent surveys by major pollsters between Aug. 21 and Sept. 10.

“True, Remain enjoys a lead in the polls. But that lead remains a narrow one, and there is little sign of it growing,” said Senior Research Fellow at The National Centre for Social Research (NatCen) John Curtice.

“It rests quite heavily on the preferences of those who did not vote two years ago, and who by two to one now say they would back Remain. Getting them to turn out to vote in any second ballot might yet prove a considerable challenge.”

London and Brussels are racing to agree a Brexit deal but Prime Minister Theresa May’s proposals have been criticized by both the European Union and Euroskeptics within her party. She has ruled out having a second referendum.

But the main opposition Labour Party is open to a second public vote with the option of staying in the bloc, its Brexit spokesman Keir Starmer said earlier this week.

Campaigners on both sides of the argument have been stepping up their efforts in recent weeks as some Brexiteers argue for a cleaner break from the EU and Remainers say ending membership as currently planned would do economic damage to Britain.