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. Britains 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 ministers 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.