Updated at 10:45 a.m. ETBritish voters are heading to polling places Thursday, in a race that Prime Minister Theresa May's Conservative Party is expected to win — but not by the wide margins that were predicted two months ago, when May called for the snap election.In polls leading up to the campaign's final day, May's lead over Labour Party leader Jeremy Corbyn was seen shrinking to 6 percentage points. Voting will close Thursday at 10 p.m. BST — or 5 p.m. ET.When May called for this election back in April, her Tories were hoping to build on their small majority in the House of Commons, where they hold 330 of 650 seats. Explaining the surprise announcement, she called it the "only way to guarantee certainty and stability for the years ahead."Thursday's vote takes place less than two weeks before the U.K. is to begin formal negotiations on leaving the European Union — the same issue that brought May into office last July, after the resignation of fellow Conservative David Cameron.While the subject of Brexit was a main issue when the vote was scheduled, much of the campaign has focused not on Brexit, but on security, after high-profile attacks on public spaces in Manchester and London. And in recent weeks, the Conservative Party's lead in polls has been cut in half."The third terrorist attack on May's watch has weakened her, especially after it came to light that she had cut 20,000 police officers as home minister," NPR's Eleanor Beardsley reports.Responding to criticism, May said this week that she'll push for tougher policies on prison sentences and deportations."If our human rights laws stop us from doing it, we'll change the laws so we can do it," May said.By contrast, Corbyn has been gaining momentum despite a widely held belief that his Labour Party won't be able to force May out of No. 10 Downing St. On Wednesday, he promised to stand up to President Trump if he's elected.As NPR's Frank Langfitt reports, "[Corbyn] has been running a kind of Bernie Sanders-esque campaign, looking for a lot more funding for the National Health Service, which has really suffered. He's offering free higher education — so, really focusing on younger voters."Both May and Corbyn were criticized for notable absences on the campaign trail. For May, it was her refusal to take part in a debate on BBC TV, leaving Corbyn to spar with other members of her party. For Corbyn, it was his no-show at an event touting Labour's populist message — feeding suspicions that rivals in his own party may have been working against him.May's voice was also used against her in a protest song that hit the Top 5 on Britain's charts, as the relatively unknown group Captain Ska interspersed May's comments on social issues with chants accusing her of lying on "Liar Liar GE2017" — referring to the general election by its initials. Copyright 2017 NPR. To see more, visit http://www.npr.org/.