LONDON — The United Kingdom will hold its first national election in almost five years on Thursday, with opinion polls suggesting that Prime Minister Rishi Sunak's Conservative Party will be punished for failing to deliver on promises made during 14 years in power.

The center-right Conservatives took power during the depths of the global financial crisis and have won three more elections since then. But those years have been marked by a sluggish economy, declining public services and a series of scandals, making the Tories, as they are commonly known, easy targets for critics on the left and right.

The Labour Party, which leans to the left, is far ahead in most opinion polls after focusing its campaign on a single word: Change.

But the Tories face other challenges as well. The new Reform Party is siphoning off votes from the rightwing of the Conservatives after criticizing the Tory leadership for failing to control immigration.

Here is a look at the election and what's at stake.

How will the election work?

People throughout the United Kingdom will elect all 650 members of the House of Commons, one for each local constituency. There are no primaries or run-offs, just a single round of voting on July 4.

Britain uses a ''first past the post'' system of voting, which means that the candidate that finishes top in each constituency will be elected, even if they don't get 50% of the vote. This has generally cemented the dominance of the two largest parties, Conservatives and Labour, because it is difficult for smaller parties to win seats unless they have concentrated support in particular areas.

How is the prime minister chosen?

The party that commands a majority in the Commons, either alone or with the support of another party, will form the next government and its leader will be prime minister.

That means the results will determine the political direction of the government, which has been led by the center-right Conservatives for the past 14 years. The center-left Labour Party is widely seen to be in the strongest position.

Who is running?

Sunak, a former Treasury chief who has been prime minister since October 2022, is leading his party into the election. His primary opponent is Keir Starmer, a former director of public prosecutions in England and leader of the Labour Party since April 2020.

But other parties, some of which have strong regional support, could be crucial to forming a coalition government if no one wins an overall majority.

The Scottish National Party, which campaigns for Scottish independence, the Liberal Democrats, and the Democratic Unionist Party, which seeks to maintain ties between Britain and Northern Ireland, are currently the three largest parties in Parliament after the Conservatives and Labour. Many observers suggest the new Reform Party, fronted by Brexit campaigner Nigel Farage, may siphon votes from the Conservatives.

Why are the Conservatives under pressure?

The Conservatives have faced one challenge after another since they took power in 2010. First there was the fallout from the global financial crisis, which swelled Britain's debt and caused the Tories to impose years of austerity to balance the budget. They then led Britain out of the European Union, battled one of the deadliest COVID-19 outbreaks in western Europe, and saw inflation soar after Russia invaded Ukraine.

Regardless of the circumstances, many voters blame the Conservatives for the litany of problems facing Britain, from sewage spills and unreliable train service to the cost-of-living crisis, crime and the influx of migrants crossing the English Channel on inflatable boats.

On top of that, the party has been tarred by the repeated ethical lapses of government ministers, including lockdown-busting parties in government offices. The scandals chased former Prime Minister Boris Johnson from office and ultimately from Parliament after he was found to have lied to lawmakers. His successor, Liz Truss, lasted just 45 days after her economic policies cratered the economy.

What are the big issues?

The economy: Britain has struggled with high inflation and slow economic growth, which have combined to make most people feel poorer. The Conservatives succeeded in controlling inflation, which slowed to 2% in the year through May after peaking at 11.1% in October 2022, but growth remains sluggish, raising questions about the government's economic policies.

Immigration: Thousands of asylum seekers and economic migrants have crossed the English Channel in flimsy inflatable boats in recent years, triggering criticism that the government has lost control of Britain's borders. The Conservatives' signature policy for stopping the boats is a plan to deport some of these migrants to Rwanda. Critics say the plan violates international law, is inhumane, and will do nothing to stop people fleeing war, unrest and famine.

Health care: Britain's National Health Service, which provides free health care to everyone, is plagued with long waiting lists for everything from dental care to cancer treatment. Newspapers are filled with stories about seriously ill patients forced to wait hours for an ambulance, then longer still for a hospital bed.

The environment: Sunak has backtracked on a series of environmental commitments, pushing back the deadline for ending the sale of gasoline- and diesel-powered passenger vehicles and authorizing new oil drilling in the North Sea. Critics say these are the wrong policies at a time the world is trying to combat climate change.

Why is the election being held now?

Sunak surprised pundits and most of his own lawmakers six weeks ago when he set the election for July 4, at least three months earlier than expected.

While most observers thought the vote would take place in the fall, Sunak gambled on a summer election, hoping that positive economic news would help him persuade voters that Conservative policies were beginning to work.

The decision was so startling that it landed the Tories in hot water. Allegations have emerged that party members and police officers assigned to protect government officials had placed wagers on a summer election, suggesting they had inside information and damaging Sunak's ability to claim that his party is more trustworthy than Labour.

Commentators had been speculating about the timing of the election for months because the parliamentary term was scheduled to end in mid-December. While each parliament is elected for up to five years, the prime minister can call an election whenever it is most advantageous politically.