But he was held upon arriving at Heathrow, and said he would be sent home within a few hours.
"I am in a detention centre at Heathrow ... I am detained," he told the Reuters news agency.
"They took my passport. I will not be allowed to enter the country. They will send me back within a few hours."
British authorities said Wilders would not be allowed entry into the UK, but gave no other details about what had happened at Heathrow.
"Any European Union ... national refused admission to the UK under immigration regulations will be detained until arrangements have been made for their removal from the UK," a Home Office spokesman said.
Wilders previously called Britain's decision "cowardly".
"This is something you expect in Saudi Arabia but not in Britain. I think this cowardly position of Britain is very bad," he said.
Lord Pearson, a peer at the House of Lords, Britain's upper house of parliament, had invited Wilders to show the film.
Fitna is an Arabic word which has numerous meanings including "sedition" and "temptation", and appears in the Quran. The film juxtaposes shots of the 9/11 attacks on the US with quotations from the Quran,
Its screening prompted protests in Pakistan, Iran, Indonesia and Afghanistan, while Ban Ki-moon, the United Nations secretary-general, described the film as "offensively anti-Islamic".
Wilders also sparked outrage over other anti-Islamic comments, including calling for a ban on the Quran and comparing Islam to Nazism.
Last month a court in Amsterdam ruled that he must stand trial for hate speech.