LONDON - Britain's Theresa May appeared on course to win a crushing election victory in June after opinion polls put support for her ruling Conservative party at around 50 percent, double that of the opposition Labour party.May's decision to call a June 8 election stunned her political rivals this week and a string of polls released late on Saturday suggested the gamble had paid off, with one from ComRes showing the party of Margaret Thatcher enjoying levels of support not seen since 1991.May, appointed prime minister in the turmoil that followed Britain's vote to leave the European Union last June, said she needed the election to secure her own mandate and strengthen her hand for the Brexit negotiations ahead.She is also looking to capitalize on the disarray swirling around the Labour party, which has been riven with internal division over its leader Jeremy Corbyn. Voters also appear to be switching from the anti-EU UKIP party, which helped campaign for Brexit, to May's Conservatives, which will likely deliver it."The announcement of a snap election has clearly focused the minds of the electorate," said James Crouch at pollster Opinium.In two other polls, May's Conservatives also gained ground in Scotland at the expense of the Scottish National Party, potentially weakening the nationalists' demand for another independence referendum.May has already warned her party not to take victory for granted, a message that was echoed by pollsters on Saturday."While no political party could ever object to breaching the 50 percent barrier for the first time this century, this spectacular headline result masks a real danger for the Tories," said ComRes Chairman Andrew Hawkins."The fact that six in ten voters believe Labour cannot win under Corbyn’s leadership bring with it the threat of complacency among Tory (Conservative) voters who may be tempted to sit at home on June 8th and let others deliver the result they expect."According to polls by Opinium, ComRes and YouGov, May's Conservatives held a lead of between 19 and 25 percentage points, with the party's support ranging from 45 percent to 50 percent.