The government has come under fire after banning a Dutch MP from entering the UK over anti-Islamic remarks.
Former Conservative cabinet minister Michael Portillo said by turning away Geert Wilders, ministers had made a "populist twit and bigot" world famous.
The Freedom Party MP had been invited to a House of Lords screening of his film, linking the Koran to terrorism.
Muslim groups backed the government's decision and labelled Mr Wilder "an open and relentless preacher of hate".
Mr Wilders, who faces trial in his own country for inciting hatred, caused outrage across the Muslim world last year when he posted his film, Fitna, on the internet.
Now he is at the centre of further controversy following an invitation from the UK Independence Party's Lord Pearson to show his film in the House of Lords.
Lord Pearson told the BBC it was a "matter of free speech" and the film would only be offensive to violent Islamists.
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 Wilders' absence, although only five peer and no MPs were present.
But Mr Portillo expressed concerns those who did attend would not be the only people to view it.
Speaking on BBC1's This Week, he said the MP held "unattractive" opinions but had he been allowed in he would have arrived "unnoticed to show his film to 30 fairly eccentric peers".
Instead, he said, he has become a "globally famous figure" with thousands of people going on the internet to watch the film.
Differences and debate
Crossbench peer Baroness Cox, who hosted a later screening for the media, accused the British government of "succumbing to threats of intimidation".
She said it was "a very sad and a very disturbing day for British democracy when a European parliamentarian has not been allowed into this country".
"I don't agree with everything that Geert Wilders has to say, but I believe he has the right to say it in a democracy."
Mr Wilders defended his visit to the UK, saying he had visited two weeks ago and planned to return in the future.
He said: "I'm not doing anything wrong. I'm not protesting or running through the streets of London.
"Democracy means differences and debate. It's a very sad day when the UK bans an elected parliamentarian."
He went on to accuse Gordon Brown of being the "biggest coward in Europe".
Mr Brown's spokesman said the prime minister fully supported the decision taken by Home Secretary Jacqui Smith.
Mohammed Shafiq, chief executive of the Ramadhan Foundation, also supported the Home Secretary's decision.
"His fascist views are not welcome in our country where we pride ourselves as a multi-faith society," he said.
"This is not about freedom of speech but about stopping the incitement to religious hatred this man promotes."
Earlier, the Muslim Council of Britain said Mr Wilders was "an open and relentless preacher of hate".
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.
Foreign Secretary David Miliband said the home secretary made a decision on an individual case.
"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," he added.
Lib Dem home affairs spokesman Chris Huhne said even with freedom of speech, there was a line to be drawn.
The Dutch government said it "regretted" the decision to bar Mr Wilders from the UK, saying it believed all its MPs "should be able to travel freely in the European Union".
Other prominent figures banned from the UK:
Muslim cleric Dr Yusuf al-Qaradawi refused entry in order to protect community cohesion. He has described suicide bombers as "martyrs" and homosexuality as "disease".
Nation of Islam leader Louis Farrakhan barred on the grounds that his allegedly racist and anti-Semitic views could threaten public order.
Martha Stewart and US rapper Snoop Dogg denied entry because of criminal convictions.
I think they were right to turn him away, as they've turned away Muslim extremists too. It sends out the right message that extremism on either end of the spectrum is not acceptable to the UK government.