Controversial Dutch MP Geert Wilders has hailed his arrival in the UK as a "victory for freedom of speech".
He told a packed press conference in Westminster he was "proud of the UK asylum and immigration tribunal" for overturning the ban.
And he repeated his criticism of Muslim ideology and defended his call for the Koran to be banned in Holland.
His press conference was moved inside amid angry scenes, with demonstrators chanting "Wilders go to hell".
About 40 Muslim protesters gathered outside the Abbey Gardens buildings, opposite the Houses of Parliament, where the hastily rearranged press conference was held.
Held back by a police line, and surrounded by camera crews from around the world, they chanted slogans such as "Sharia for the UK" and "Freedom go to hell" and held up placards saying: "Sharia for the Netherlands" and "Islam will be superior".
One protester, Sayful Islam, said they wanted to see Mr Wilders "tried in an Islamic court" for "insulting the Prophet", adding: "We need to put this dog on a leash".
He described Mr Wilders as "the open voice of democracy" and claimed the Dutch MP's views were shared by "every government in Europe".
I feel that the more Islam that we get in our societies the less freedom that we get
Mr Wilders said he was not setting out to insult Muslims - the majority of whom were "law-abiding" - but he defended his right to criticise the actions of a minority who he said posed a threat to society.
"My aim is not to insult anyone but it is to defend freedom," he said.
Asked about the protests that greeted his arrival in Westminster, he said: "I am very proud that people - even if they totally disagree with me - can use their democratic right to protest."
Explaining his views on Islam, he said: "I have a problem with the Islamic ideology, the Islamic culture, because I feel that the more Islam that we get in our societies the less freedom that we get."
He denied his abortive attempt in the Dutch Parliament to get the Koran banned flew in the face of his commitment to free speech.
"Even in the United States, where they have a first amendment, there is one red line, which is the incitement of violence and this was exactly my point," he told reporters.
He also denied responsibility for the publicity which has greeted his visit, saying: "If anybody has responsibility for this publicity it is the UK government and the home secretary and not Geert Wilders."
Mr Wilders, who faces trial at home for inciting hatred, was allowed into the UK after a ban on him was lifted.
The Freedom Party leader was turned away from the UK in February on the grounds that his allegedly anti-Islamic views posed a threat to public security but that decision was overturned earlier this week.
Although agreeing not to challenge the decision, the Home Office has said Mr Wilders' comments will be closely watched by the authorities.
Mr Wilders was invited to the UK by UK Independence Party peer Lord Pearson.
Asked whether he too wanted to ban the Koran, he said: "I disagree with Geert in fact, who has said that if Mein Kampf is banned in Holland, then so the Koran should be banned. I don't agree with that at all.
"I want the Koran discussed very much more and I want it particularly discussed by the 98% or whatever it is of the Muslim community who are mild, peace-loving people.
"But what I want them to do is to get up off their bottoms and take on their violent co-religionists who do base these acts of evil on the Koran."
When he tried to visit the UK in February, Mr Wilders was back by immigration officials at Heathrow airport on the grounds that his views could stir up "inter-faith violence".
Nicknamed "Mozart" because of his mane of platinum blond hair
Voted politician of the year in 2007 by the Dutch political press,
Lives under police protection because of death threats
Wants the Koran and the full-length garment, the burka, to be banned
However, on Tuesday the Asylum and Immigration Tribunal ruled there was no evidence to suggest he represented a real and serious threat to the "fundamental interest" of society.
The judges said that even if there had been evidence, it would still have been wrong to turn him away because in the event of any trouble the police would have been able to deal with it.
The Home Office said Mr Wilders' statements and behaviour during his visit "will inevitably impact on any future decisions to admit him".
Officials say his case differs from that of a larger number of individuals - including Islamic extremists and white supremacists - who are on a list of people excluded from Britain for "unacceptable behaviour".
The power to impose such exclusions was introduced in 2005, following the London bombings, and applies predominantly to non-EU nationals who would seek to "foster hatred or promote terrorism".
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