By Kate Holton and William James LONDON (Reuters) - British Muslim leaders urged people to contact police if they knew the identity of the man with an English accent who appeared in a video showing the beheading of an American journalist. The Muslim Council of Britain, the largest Muslim umbrella group in the country, condemned the "abhorrent murder" of James Foley in Syria and called for united action by Muslims to stop the "poison of extremism" infiltrating their communities. Prime Minister David Cameron said on Wednesday it looked increasingly likely that the man in the Islamic State video was British, one of hundreds who have traveled to Syria to fight. "We are horrified at the abhorrent murder of James Foley, a reporter who initially went to the region to expose the human rights abuses of the Syrian regime." Iqbal Sacranie, an adviser to the council, told London's Evening Standard newspaper that anyone who recognized the man had a duty to contact police.