MAIDENHEAD, England, April 21 (Reuters) - British Prime Minister Theresa May said on Friday that she was not taking anything for granted as she geared up for a snap election in June, in which polls suggest her Conservative party was heading for a landslide victory. May called the national election in a surprise move on Tuesday, saying it was necessary to boost her majority and provide stability as Britain gears up for two years of negotiations with the European Union about its departure from the bloc. Polls give May's governing Conservative party a lead of around 20 percentage points, enough to potentially give her a parliamentary majority of more than 100 seats, but May said she was not complacent. "The election campaign has only just begun. I'm not taking anything for granted. The result is not certain," she said in a speech at a GlaxoSmithKline factory in her electoral area of Maidenhead, west of London. The Labour party has been riven by divisions over its leader Jeremy Corbyn and Brexit, while May's commitment to a clean break with the EU has undermined support for the eurosceptic UK Independence Party. SPENDING PLEDGES While many specific policy positions have yet to be filled out, both May and her finance minister, Philip Hammond, gave the first indications on how the party's spending plans on key voter issues like foreign aid, pensions and tax will look. May reaffirmed a commitment on foreign aid spending - a pillar of predecessor David Cameron's attempts to soften the image of the Conservative party. May said that the pledge to spend 0.7 percent of national income on foreign aid would remain. Media reports had said it would be scrapped in the Conservatives' election manifesto amid opposition from some lawmakers and newspapers who said it should be spent at home instead. "Let's be clear - the 0.7 percent remains, and will remain," she said. "What we need to do, though, is to look at how that money is spent, and make sure that we are able to spend that money in the most effective way." Former Archbishop of Canterbury Rowan Williams, who chairs the charity Christian Aid, had earlier called on May to wear the commitment as a "badge of honour". Microsoft co-founder Bill Gates has also called for spending to be maintained. May avoided committing to renew the government's policy of increasing old-age pensions by a minimum of 2.5 percent each year, when asked to do so by a reporter. That position was echoed by Hammond, speaking in Washington, who said the government had solved the problem of pensioner poverty. Hammond also said that 2015 manifesto commitments not to raise key taxes, made before he was appointed, were hampering his ability to manage the economy.