There were calls for him to be replaced after he attended the Everest business conference in Katowice on 29 May.

Uefa said after an investigation that "we unequivocally reject the values promoted by a group linked to this conference".

Marciniak, who refereed the World Cup final between Argentina and France in December, said he had been "gravely misled" and "completely unaware" about the affiliations of the conference.

"I want to express my deepest apologies for my involvement and any distress or harm it may have caused," he said in a statement.

Poland's Never Again anti-racism association had called on the referee to distance himself from far-right activities.

Mentzen, co-chairman of the far right and libertarian Confederation party, has focused on his libertarian economic views in recent times but caused controversy in 2019 when he announced his five-point slogan, which was anti-Semitic and homophobic.

He had said the business conference had "nothing to do with politics", and called the "denunciation" of Marciniak "absurd".

The Polish sports minister Kamil Bortniczuk and the country's deputy foreign minister also defended the referee.

Marciniak said: "Upon reflection and further investigation, it has become evident that I was gravely misled and completely unaware of the true nature and affiliations of the event in question. I had no knowledge that it was associated a Polish extreme-right movement.

"Had I been aware of this fact, I would have categorically declined the invitation. It is important to understand that the values promoted by this movement are entirely contrary to my personal beliefs and the principles I strive to uphold in my life. I am deeply remorseful for any perception that my participation may have contradicted them.

"I wholeheartedly condemn any form of hate, discrimination, or intolerance, as they have no place within the sport or society as a whole.

"Moving forward, I pledge to be more vigilant in scrutinising the events and organisations with which I associate myself. I am committed to learning from this experience and ensuring that such lapses in judgment do not occur in the future.

"Lastly, I extend my sincere apologies to the clubs, players, fans, colleagues, officials and organisations who place their trust in me. I fully comprehend that my actions have had repercussions beyond personal disappointment, and I am fully prepared to accept any consequences resulting from my ill-advised participation."

Uefa investigated the incident and said it acknowledged Marciniak's apology and said the Never Again group "requested that Marciniak remain in his role... firmly asserting that removing him would undermine the promotion of anti-discrimination".

"Based on the information provided, Uefa confirms that Marciniak will fulfil his role as the referee for the Champions League final," European football's governing body said.

In a letter to Uefa president Aleksander Ceferin, Bortniczuk said the business conference had nothing to do with politics and that the referee had delivered a 45-minute inspirational talk at the conference. Bortniczuk said the referee had no contact with the far-right leader at the conference.

Polish deputy foreign minister Pawel Jablonski said untruthful accusations against Marciniak are "an immense scandal".

The Confederation party has nine MPs in the Polish parliament - Mentzen is not one of those. In recent polls, it has placed as high as third before this autumn's parliamentary elections. The party draws much of its support among young men.