The organisers, the European Broadcasting Union (EBU), say it would breach its political impartiality.

But Downing Street said it would be "fitting" for Mr Zelensky to speak given Russia's invasion of his country.

Labour leader Sir Keir Starmer is also calling for the Ukrainian leader to be allowed to make a speech.

Ukraine was meant to be hosting this year's Eurovision after winning it last year, but it is taking place in Liverpool instead after Russia's invasion.

It has been reported that Mr Zelensky wanted to make a video appearance at the contest's final on Saturday, to an expected global audience of 160 million.

But in a statement on Thursday, the EBU said it had turned down a request from the Ukrainian president to address the event, despite his "laudable intentions".

"The Eurovision Song Contest is an international entertainment show, and governed by strict rules and principles," it added.

"As part of these, one of the cornerstones of the contest is the non-political nature of the event. This principle prohibits the possibility of making political or similar statements as part of the contest."

BBC Director General Tim Davie told the BBC's Eurovisioncast he understood the EBU's decision and that throughout its history, Eurovision "has not been a platform for political statement".

But he stressed the BBC was hosting on behalf of Ukraine and that it is "a celebration across Europe for freedom, for democracy".

'Values and freedoms'

The EBU said that a Ukrainian design agency had been involved in designing artwork for the event, and 11 Ukrainian artists, including last year's winners Kalush Orchestra, would be performing.

However, Mr Sunak's spokesman questioned the decision not to have Mr Zelensky speak, saying: "The values and freedoms that President Zelensky and the people of Ukraine are fighting for are not political, they're fundamental."

His spokesman argued that Eurovision "themselves recognised that last year" by banning Russian artists from participating.

However, he added that the prime minister had no plans to intervene and ask broadcasters to change their mind.

Ukraine's ambassador to the UK, Vadym Prystaiko, said the final of the contest would have been a "great moment" for Mr Zelensky to address a huge audience.

But speaking to PA Media, he added: "We understand all the internal politics and the unbiased sort of approach to all this, that's why we don't have to push too much."

Ukraine will be represented at this year's contest by Nigerian-Ukrainian pop duo TVORCHI

In statement, Labour leader Sir Keir Starmer said: "It's vital that we all continue to keep the plight of the Ukrainian people front of mind as they stand up to Russian aggression on behalf of us all.

"Eurovision is an expression of international unity and freedom, and President Zelensky should be able to address it as a great defender of both."

Russia ban

The EBU initially said it would allow Russia to participate in the 2022 final, following its invasion of Ukraine two months before it was due to be held in Italy.

But it then changed course within 24 hours, saying that allowing Russia to take part would "bring the competition into disrepute".

UA:PBC, Ukraine's public broadcaster, as well as those from Iceland, Finland, Norway and the Netherlands, had called for Russia to be banned.

Boris Johnson, who was British prime minister during Russia's invasion and oversaw the UK's initial response, said "it would have been right to hear" from him during the final on Saturday.

Formed in 1950, the EBU has 68 broadcasting organisations as members, including the BBC - which is hosting this week's finals and semi-finals.