LONDON, May 22 (Reuters) British Prime Minister Theresa May will today urge voters to back her to deliver the country's exit from the European Union, playing one of her strongest cards in the election campaign as opinion polls show that her party's large lead has shrunk. A series of polls ahead of Britain's June 8 election have shown the Conservatives' lead over Jeremy Corbyn's Labour Party has fallen to between 9 and 13 percentage points, well down on leads of 20 points or more before May called the snap election. After launching her manifesto last week, including unexpected plans to reduce financial support for elderly voters, May returned to her core message, saying that Corbyn was not committed to or capable of securing a successful Brexit. "The deal we seek will be negotiated by me or Jeremy Corbyn. There will be no time to waste and no time for a new government to find its way," May will say, according to extracts of a speech that will highlight that divorce talks with the EU could begin 11 days after the election. EU officials are preparing for Brexit talks to begin on June 19 but expect confirmation of the date only after the British vote. Although both May and Corbyn campaigned last year to remain in the EU, polls show that May is more trusted to secure a good deal in talks with Brussels and that some voters are confused about Labour's position on the issue. Last week Corbyn promised to tear up May's Brexit strategy prioritising control over immigration by promising to leave the European single market. He pledged instead to focus on protecting jobs, preserving living standards and retaining access to the single market. However, Corbyn has been criticised by some Labour voters for not opposing May's EU exit strategy strongly enough and by others for not embracing Brexit more enthusiastically. "We need someone representing Britain who is 100 percent committed to the cause," May will say. "Not someone who is uncertain or unsure, but someone utterly determined to deliver the democratic will of the British people." REUTERS AKC 0624