A voter enters into a polling station after UK's general election kicks off on June 8 in London, UK. Photo by Angel Kong/China Daily Europe

There are 46.9 million registered voters in the UK and they will vote to choose 650 members of Parliament to represent them. In theory, if one party gets at least 326 MPs, it will be able to form a government. If the largest party gets less than 326, it may have to form a coalition.

As Sinn Fein MPs from Northern Ireland and MPs appointed to the Speaker's office don't vote, the actual minimum number of seats for a practical majority is 322.

Wednesday opinion polls suggest that May's Conservatives are so far the favorite to win, leading the Labour Party by between 6 and 9 percent. The Liberal Democrats and the United Kingdom Independence Party trail far behind with around 8 and 5 percent.

The election in Scotland will be dominated by the Scottish Nationalist Party and in Northern Ireland by Sinn Fein and the Democratic Unionist Party.