Investors bet Britain will remain in the EU

Eurozone vs. EU: What's the difference?
Eurozone vs. EU: What's the difference?

Investors are growing more confident that the U.K. will vote to remain in the European Union, sending the pound and stocks higher.

Brits began voting at 2 a.m. ET on Thursday in a historic referendum on whether the U.K. should remain a member of the 28-nation bloc, or become the first country to leave.

By 11 a.m. ET, the pound was flat after earlier hitting $1.49 -- its highest level against the U.S. currency since December 2015. The euro was edging up against the dollar, and European stock markets gained more than 1%. U.S. stocks rose about 1%.

London's FTSE 100 index was also higher, although it trimmed some of its early gains late in the session.

"The overall mood across markets remains firmly positive ... although the U.K.'s top 100 index has shed most of the day's advances. Given that it has advanced so strongly in recent days, that is hardly surprising," said Chris Beauchamp, senior market analyst at IG.

Markets have been volatile during the referendum campaign, as investors have speculated about the impact a U.K. split from the EU could have on stocks and the economy.

The pound in particular has swung wildly in response to opinion polls. It has gained nearly 5% since hitting a low of $1.41 last week. The FTSE 100 has gained 6% in five days.

EU referendum: complete coverage

Two new surveys conducted Tuesday and Wednesday, but released Thursday, showed a lead for the remain camp, as does the average of the six most recent opinion polls.

A "barometer" of live betting odds published by the firm Ladbrokes put the chances of a vote to remain at 86%.

Why you should care about Britain's EU vote

Immigration and the economy have been cited by voters as the main issues in their decision.

Campaigners for a British exit (Brexit) say the U.K. can only control immigration if it leaves the EU, which insists on free movement of people across the union. Campaigners for Britain to remain an EU member say walking out of the biggest free trade area in the world would do irreparable damage to the economy.

A non-Brits guide to the referendum

-- Alanna Petroff contributed to this article.

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