LONDON, April 18 (Reuters) - British Prime Minister Theresa May called on Tuesday for an early election on June 8, saying she needed to strengthen her hand in divorce talks with the European Union by shoring up support for her Brexit plan.

Standing outside her Downing Street office, May said she had been reluctant about asking parliament to back her move to bring forward the poll from 2020, but decided it was necessary to try to prevent opposition parties “jeopardizing” her work on Brexit.

Some were surprised by her move - she has repeatedly said she does not want to be distracted by time-consuming campaigning - but opinion polls give her a strong lead, the economy is weathering the Brexit vote and she has faced opposition from her own party for some of her domestic reforms.

The pound rose to a two-and-a-half-month high against the U.S. dollar after the announcement, as forex markets bet ― initially at least ― that May would strengthen her parliamentary majority. Britain’s main share index fell to its lowest point in more than seven weeks.

“It was with reluctance that I decided the country needs this election, but it is with strong conviction that I say it is necessary to secure the strong and stable leadership the country needs to see us through Brexit and beyond,” May said.

“Every vote for the Conservatives will make it harder for opposition politicians who want to stop me from getting the job done.”

Britain joins a list of western European countries scheduled to hold elections this year. Votes in France in April and May, and in Germany in September, have the potential to reshape the political landscape around the two years of Brexit talks with the EU expected to start in earnest in June.

May is capitalizing on her runaway lead in the opinion polls. The Conservative Party is around 20 points ahead of the main opposition Labour Party, a large lead for an incumbent party two years after the last parliamentary election.

The prime minister’s own personal ratings also dwarf those of Labour leader Jeremy Corbyn, with 50 percent of those asked saying she would make the best prime minister. Corbyn wins only 14 percent, according to pollster YouGov.

Stefan Wermuth / Reuters Britain's Prime Minister Theresa May speaks to the media outside 10 Downing Street, in central London, Britain April 18, 2017.

‘HITCHCOCK’

Some voters questioned on social media whether they wanted to cast yet another ballot less than a year after the June referendum on EU membership and two years after they voted in the last parliamentary poll.

Business groups expressed concern that the government’s focus may stray away from the economy. Adam Marshall, director general of the British Chambers of Commerce, called for reassurance that “the key challenges facing the economy will be front and center throughout any election period.”

European Council President Donald Tusk, who is running the negotiations with Britain, said the election was a Brexit plot twist worth of master of suspense Alfred Hitchcock.

First, May must win the support of two-thirds of the parliament in a vote on Wednesday, which looked certain after Labour and the Liberal Democrats said they would vote in favor.

Corbyn welcomed the election plan. “In the last couple of weeks, Labour has set out policies that offer a clear and credible choice for the country. We look forward to showing how Labour will stand up for the people of Britain,” he said.

Nicola Sturgeon, first minister of the Scottish government, described the decision as a “huge political miscalculation” that could help her efforts to hold a new independence referendum.

May, a former interior minister, was appointed prime minister after Britain’s vote to leave the European Union forced the resignation of her predecessor David Cameron. The election will be a vote on her performance so far.

Her spokesman said she had the backing of her top team of ministers and had informed Queen Elizabeth of her plans on Monday.

If the opinion polls are right, she will win a new mandate for a series of reforms she wants to introduce in Britain and also a vote of confidence in a vision for Brexit which sees the country outside the EU’s single market.

She urged voters to back her plan, saying other parties may try to destabilize Britain at crucial points in the EU talks.

“The decision facing the country will be all about leadership,” May said. “What they are doing jeopardizes the work we must do to prepare for Brexit at home, and it weakens the government’s negotiating position in Europe.”

(Additional reporting by Elisabeth O’Leary in Edinburgh, Kate Holton and Andy Bruce in London, editing by Sonya Hepinstall)