Union flags and the Big Ben clocktower cover notebooks are seen on sale in London, Britain, Thursday December 17, 2015. REUTERS/Luke MacGregor

LONDON (Reuters) - The campaign for Britain to leave the European Union saw its lead grow slightly over the rival “In” campaign, according to a weekly online poll published by opinion poll firm ICM on Monday.

The poll found 46 percent would vote “Out”, up one percentage point from the previous ICM poll on May 3, while 44 percent would support staying in the bloc, unchanged from the previous survey.

The poll, weighted by ICM to take into account the likelihood of respondents to vote in the referendum and carried out between May 6 and May 8, found 11 percent were undecided.