A Dutch MP who called the Koran a "fascist book" has been sent back to the Netherlands after attempting to defy a ban on entering the UK.
Freedom Party MP Geert Wilders had been invited to show his controversial film - which links the Islamic holy book to terrorism - in the UK's House of Lords.
But Mr Wilders, who faces trial in his own country for inciting hatred, has been denied entry by the Home Office.
He told the BBC it was a "very sad day" for UK democracy.
The Dutch ambassador was also at Heathrow to make clear his government's opposition to the ban on Mr Wilders entering the UK.
Mr Wilders' film Fitna caused outrage across the Muslim world when it was posted on the internet last year.
After being questioned at Heathrow, the MP said he had been to the House of Lords two weeks ago and there had been "no problem".
He added: "I'm not doing anything wrong. I'm not protesting or running through the streets of London."
Mr Wilders added: "Democracy means differences and debate. It's a very sad day when the UK bans an elected parliamentarian... Of course I will come back."
He said the government's actions had proved that Gordon Brown was the "biggest coward in Europe".
Mr Brown's spokesman said the prime minister "fully supports the decision" taken by Home Secretary Jacqui Smith.
Mr Wilders was invited to the House of Lords for a screening of Fitna by the UK Independence Party's Lord Pearson.
The peer said it was a "matter of free speech", telling the BBC: "We are going to show it anyway because we think MPs and peers should see this film."
He added: "The film isn't offensive unless you are a violent Islamist. Most of my Muslim friends think it's a very good film."
Fitna's opening scenes show a copy of the Koran followed by footage of the 9/11 attacks in the US and the bombings in Madrid in 2004 and London in 2005.
The Lords screening went ahead as planned, despite Mr Wilder's non-attendance.
BBC political correspondent Iain Watson said about 30 people had been at the screening and had given a round of applause, while calling for a debate on the issues raised.
The Dutch prime minister has said the film serves "no purpose other than to offend".
Foreign Secretary David Miliband told the BBC's Hardtalk: "The home secretary made a decision on an individual case as she is required to do."
He added that the film contained "extreme anti-Muslim hate and we have very clear laws in this country".
Mr Miliband also said: "We have profound commitment to freedom of speech but there is no freedom to cry 'fire' in a crowded theatre and there is no freedom to stir up hate, religious and racial hatred, according to the laws of the land."
The Home Office said there was a blanket ban on Mr Wilders entering the UK under EU laws enabling member states to exclude someone whose presence could threaten public security.
"The government opposes extremism in all forms," it said in a statement, adding that it had tightened up rules on excluding those engaging in "unacceptable behaviour" in October.
The home secretary has the power to stop people entering the UK if she believes there is a threat to national security, public order or the safety of UK citizens, but she cannot exclude people simply because of their views.
Earlier this year, a Dutch court ordered prosecutors to put the MP on trial for inciting hatred and discrimination by making anti-Islamic statements.
Labour peer Lord Ahmed, who expressed his concerns to the parliamentary authorities about Mr Wilders' visit, told the BBC: "This man doesn't have any respect for law. He's doing this for publicity and he's seeking that and getting that."
He added: "If this man was allowed into this country it would certainly cause problems within communities around Britain."
The Muslim Council of Britain said Mr Wilders was "an open and relentless preacher of hate".
Lib Dem home affairs spokesman Chris Huhne said: "Freedom of speech is our most precious freedom of all, because all the other freedoms depend on it.
"But there is a line to be drawn even with freedom of speech, and that is where it is likely to incite violence or hatred against someone or some group."
"Fitna" could barely be called "movie". Rather, it is a mix between various common sense personal appreciations of the "author", put in a Power Point graphical background. YouTube is plenty of such "masterpieces". In fact, I think this Duth MP was looking for some popularity and found the recipe for getting a wider media coverage by using the window of opportunity opened by the scandal of the Dutch cartoons. He used the case of Islam , because he seized the opportunity, not by deep belief. And, by this, is more harmful.