Paris - European governments from across the political spectrum have in the last months found themselves increasingly challenged on the streets by popular protest movements.

These tensions are set to come to a head when EU states hold elections for the European Parliament, where populist forces are hoping to make big gains against established parties.

Protest movements have taken on many different forms in Europe, from the "yellow vest" protesters who have rattled French President Emmanuel Macron to the thousands who rallied in Slovakia after the death of an opposition journalist.

Here is a rundown of some of the main protest movements in Europe as EU states prepare to vote from May 23-26:

- Britain -

The vote for Britain to leave the EU was itself seen as a slap in the face for the political establishment, after the leaders of all main political parties at the time came out against Brexit.

With Prime Minister Theresa May now seeking to implement Brexit, hundreds of thousands of people swamped central London on March 23 to press for Britain to stay in the bloc, in one of the biggest protests seen in the capital in years.

But others have also taken to the streets to demand that Brexit be implemented and press the government not to opt for a soft exit from the EU.

- France -

The "yellow vest" movement erupted in November 2018 as a show of anger against the perceived lack of concern on the part of Macron for the problems of ordinary French.

The protests rapidly morphed into a nationwide movement against inequality and have frequently turned violent, with authorities accusing radical protesters of acts of criminal aggression.

Macron has acknowledged that some of the protesters' demands were just, and embarked on a vast nationwide debate to hear people's grievances.

In late April he promised a range of measures for easing the burdens for those worst-off, after unveiling in December a minimum wage top-up and other financial relief valued at 10 billion euros ($11 billion).

- Hungary -

Prime Minister Viktor Orban, who has proudly promoted himself as a nationalist-conservative scourge of liberalism, has become one of the most polarising figures in the country's post-Soviet history.

His policies, including labour reforms denounced as a "slave law" and a crackdown on immigration, have prompted regular protests drawing thousands of people in Budapest and other cities.

One of the biggest protests saw 15,000 people gather in central Budapest on December 16.

- Slovakia -

The assassination of investigative reporter Jan Kuciak and his fiancee in February 2018 as he was about to publish a story on alleged ties between Slovak politicians and the Italian mafia, prompted protests on a scale never seen before in Slovakia.

The protests brought down the government of prime minister Robert Fico and sparked a political transformation that culminated in the election this year of anti-corruption campaigner Zuzana Caputova as president.

- Poland -

The fatal stabbing in Poland of Gdansk's liberal mayor Pawel Adamowicz in January prompted one of the biggest gatherings seen in the country since the Solidarity movement helped bring down communism.

Tens of thousands of people gathered in January for the funeral of Adamowicz, who had been mayor of the Baltic port city for 20 years.

His killing became a lightning rod for anger against the conservative Law and Justice party (Pis), which is despised by opponents notably for a series of controversial legal reforms that have drawn rebukes from the European Union.

- Germany -

The far-right and Islamophobic Pegida has taken its fight to the streets with protests especially in the east of the country, sometimes in alliance with the far-right AfD party.

Last year, 8,000 people answered a joint call by the AfD and Pegida to protest in the Saxony city of Chemnitz. A smaller counterprotest of liberals was called in response, and a dozen people were wounded in clashes.

The tensions underscored the divisions in Germany over Chancellor Angela Merkel's decision three years ago to keep the country's borders open to asylum seekers, many fleeing war in Syria and Iraq.

- Spain -

Spain's radical leftwing Podemos party was born from the protest movement that swept the country during the financial crisis and established itself in parliament starting in 2015.

It is now challenged by another radical upstart from the other side of the political spectrum, the ultra-nationalist Vox movement, which denounces Islam and liberalism.

Vox scored a major breakthrough by winning just over 10 percent of the vote in April elections. Podemos, which took around 14 percent, could help the ruling Socialist party remain in power.

By Stuart Williams