BRUSSELS/STRASBOURG (Reuters) - A poll for the European Parliament showed that last-minute British participation in next month’s elections to the European Union’s legislature means eurosceptic groups will gain ground but pro-EU parties will keep a majority.

An election campaign poster for the upcoming European Parliament elections depicting German Justice Minister Katarina Barley, the Social Democratic Party (SPD) top candidate, is pictured in Berlin, Germany April 10, 2019. The words on the posters read "solidarity." REUTERS/Fabrizio Bensch

WHO’S VOTING AND FOR WHAT?

Some 400 million people in the European Union’s 28 member states can vote from May 23 to 26 -- including nearly 50 million Britons who were due to leave the bloc in March. Their votes for 73 lawmakers who may have to quit within weeks has upset some calculations following a delay to Brexit agreed last week.

By proportional representation, Europeans will elect 751 members to the European Parliament, which divides its time between Brussels and Strasbourg. Ranging from Malta with six seats to Germany with 96, for five years the MEPs will check and amend laws proposed by the European Commission, subject to approval by national governments in the EU Council.

WHAT’S AT STAKE?

campaign issues range from spending -- though the EU budget is equal to just 1 percent of member states’ gross domestic product -- to climate change and labour rights. But some who want the EU broken up see it as a Brexit-style referendum on the EU’s very survival, pitting advocates of historic, ethnic-based nations against the idea of pooling sovereignty to defend Europe’s wealth and values in a world of rising authoritarian powers and global corporations.

Caught up in this centre-versus-states debate are refugees. Nationalists blame the EU for a surge in arrivals in 2015. Federalists say only cooperation can control migration.

Leaders of some eastern states such as Hungary and Poland slam Brussels over migrants and its complaints that they are undermining EU rules on democracy in Warsaw and Budapest; some westerners speak of cutting their EU subsidies in retaliation.

The election in Britain is considered a new referendum on Brexit by some, one that could help block withdrawal -- or accelerate it.

ARE THERE EU POLITICAL PARTIES?

Yes. And no. Eight party groups sit in the chamber. The centre-right European People’s Party (EPP) has 29 percent and ensures an establishment majority by often cooperating with the centre-left Socialists and Democrats (S&D -- 25 percent) and ALDE liberals (9 percent). Two right-wing, anti-EU groups led by Britain’s UKIP and France’s National Rally share 10 percent.

But all the groups are unruly, and EU elections are mainly contested by national parties on issues familiar to voters.

IS BRITAIN A PROBLEM?

Some EU officials think it might be better to delay approving key post-election appointments until after British MEPs leave, to avoid accusations parliament’s decisions will lack legitimacy.

The British vote will favour eurosceptics, socialists and Greens but hurt the EPP, which has no members in Britain since the ruling Conservatives quit the group to form their own bloc.

By taking part, Britain has forced the EU to postpone the redistribution of 27 of its 73 seats to other countries. France, for example, will elect 79 MEPs, five more than it has now, but five of them will not be able to take up their seats until after Britain leaves and Parliament shrinks by 46 members to 705.

DOES THE WINNER GET TO RUN THE EU?

Not really. Well, maybe. Parliament’s leaders say they are the heart of European democracy. National leaders scoff at the 43 percent turnout in the 2014 EU elections. In practice, states wield most power and little happens that big countries dislike.

The EU executive Commission is led by Jean-Claude Juncker of Luxembourg. A historic power struggle between Parliament and Council will get an airing in the election. Parliament has pledged to force the Council to nominate as Juncker’s successor a lead candidate from a winning party in the vote. Leaders such as French President Emmanuel Macron say they won’t be bound by that. Parliament could reject the Council’s Commission nominee.

I’M CONFUSED. SO WHO REALLY RUNS THE EU?

It’s complicated. But the voting and lead candidate rumpus is part of horse-trading among governments to get compatriots or allies into top positions, not just in the Commission and Council but also in the European Central Bank.

Germany and France, the two biggest states, have the most clout, but even the smallest can play. Juncker is the third EU chief executive from little Luxembourg.

AND SO WILL THE ELECTIONS CHANGE MUCH?

A push by eurosceptics could mean a bigger, more cohesive minority to disrupt EU legislation. But EU optimists also say a campaign that grabs more people’s attention could reinvigorate post-Brexit efforts to pull the EU together.

Polls suggest the far right could increase its share but probably not enough to sound the death knell of the EU. It seems improbable that either camp, for or against closer integration in Europe, can land a knockout blow.