Tariq Ramadan has been described as a Muslim Martin Luther, but he remains banned from the United States as an extremist judged to have provided material support to terrorist organisations.

He is an Oxford University professor ranked by both Prospect and Foreign Policy as number eight in the list of the world’s top contemporary intellectuals and by Time magazine as one of the 100 most important innovators of the 21st century.

Yet he is disparaged by some as a dangerous pin-up pied piper, who can draw up to 12,000 people to his lectures, An Islamic extremist or the one man to save us all from the clash of civilisations?

A courageous reformer or a slippery double dealer who trims his arguments according to his audience? Few academics in Oxford’s recent history can have provoked such violently contrasting opinions as this visiting fellow to St Anthony’s College.

Even the Sun has had trouble making up its mind.

Soon after running a front page story inviting its readers to “meet Islamic militant Professor Ramadan”, it was proclaiming him as “a hero of young Muslims”.

Here in Oxford, at least at the Faculty of Theology where he teaches, there are no such lingering doubts about his role in our troubled world or his real motivation for being here.

While it is difficult to think of another Oxford theology teacher to have both made page one of the Sun and to have argued with Nicolas Sarkozy about the stoning of adulterers on television, Prof Ramadan’s background makes him well suited to Oxford.

Born in Switzerland in 1962, the grandson of Hassan al Banna, the founder of the Muslim Brotherhood, Prof Ramadan studied philosophy, literature and social sciences at the University of Geneva and Arabic and Islamic studies for his PhD.

He is a scholarly European Muslim, whose books, grounded in Islam’s textual sources, show him to be a skilled interpreter of Islamic history.

But it is his mission to reform Islam in the light of its complex relationship with the West that has resulted in his status as a celebrity academic.

And it is not only newspaper editors and television news producers who are anxious to seek his views on anything from violence in Gaza to Sharia.

He is an advisor to the European Union and was invited on to a task force on extremism set up by Tony Blair in the aftermath of the July 7 bombings in London.

“I want to be an activist professor,” he says.

Pursuing his ambition means that he is one of the hardest Oxford University figures to track down, as likely to be in Holland, where he is also a visiting professor at Erasmus University, or Brussels, where he is president of the think-tank European Muslim Network.

Soon he hopes America will be back in his travel plans.

“I was banned in 2004. For two years I was given no reason,” he said, when we met at the Examinations Schools in a conversation I never expected to have with an Oxford professor.

Ultimately, he learnt it was for giving 500 Euros to an organisation that had not been banned in Europe, and was not outlawed in America when he had made his contribution.

“As a result of the presidential election I think things are going to change. Discussions are now taking place with the new administration. As a result of the controversy, I became well known over there. In the Islamic world it was exactly the same. Because I was banned by Bush, I was a hero.

“When I called for a moratorium on the death penalty and corporate punishment, I was called a traitor by some Muslims, who said that I was westernising Islam. In a world of polarisation, if you try to build bridges, you will have people at you from both sides.

“I am not happy with controversy. But I am happy if people read my books and Google my name and try to understand what I’m trying to promote.”

But look him up on the internet and you may well be greeted with “Forty Reasons Why Tariq Ramadan is a bigot” or perhaps “Do You Trust This Man?”.

Somehow, last week his name emerged in reviews of the Panorama programme that claimed British policy towards Islamic radicalism was about to get a lot tougher.

Melanie Phillips, writing in The Spectator, typically, did not pull her punches, saying: “Can anyone really imagine, for example, ministers who forbid even using the term ‘Islamic terrorism’ ceasing to throw money in the direction of Tariq Ramadan, the charismatic but slippery poster-boy for ‘modernising Islam’ whose real agenda is actually the Islamising of modernity — and who is such a favourite within Britain’s security establishment because of his pied piper appeal to young British Muslims?“ In France, his angry television exchanges with Sarkozy, over rioting in the Parisian suburbs, when the French president was a minister, appear to have had long-term consequences, for he continues to be regarded with suspicion by the French authorities.

He tells me that he is becoming used to his meetings in France being suddenly cancelled, remarkably putting it down to pressure from the French intelligence services.

“They don’t let me speak, in a very subtle way. It is not direct. I’m not banned. I enter the country, I have a room — a venue — then two days before, it is cancelled. It is unacceptable. Twenty-six times in the last three years this has happened. It is incredible that this is happening in Europe. Freedom of speech is a real challenge over there. It is exactly opposite to what is happening in the UK, where I am welcome.”

He was, at least, to enjoy a courteous welcome earlier this month in Rome, where he met the Pope.

The meeting was organised as part of the ongoing efforts to build bridges between Islam and the Vatican in the aftermath of Pope Benedict’s controversial lecture in Germany, delivered two years ago, in which the Pope quoted a 14th-century Byzantine emperor on the teachings of the prophet Muhammad.

“It was good as a first step,” Prof Ramadan said. ”We talked about our common values, and that is very important.”

But Prof Ramadan remains convinced that the Pope’s controversial comments had “reduced” the importance of Islam’s European past because “he is scared of the Muslim presence in Europe”.

“It is not new. I knew him when he was Cardinal Ratzinger. This is what he thinks: that there could be a danger to the roots of Europe as a Christian continent. I understand that. It is, however, wrong not to acknowledge that the Islamic philosophical and theological tradition are part of Europe. Islam is a European religion.”

You wonder how many of his harshest critics will get to read his new book Radical Reform: Islamic Ethics and Liberation, just published by OUP.

But, then, having tried to get to to grips with it myself, I was left wondering who, outside university theology departments, will be clever enough to plough through the book’s complex theoretical sections, with a study of “the fundamentals of usul al-fiqh”, all the outcome “of a long, deep immersion in the universe of the Islamic sciences”.

For years he has argued that fellow Muslims should participate fully in the civil life of the Western societies in which they live.

But his new book extends the call for radical reform to Muslim societies and communities everywhere. If reform is achieved, it is going to require contributions from both scholars of Muslim texts and the engagement of the Muslim masses, he maintains.

In essence, it is an argument for a less literalist approach to Islamic texts, while also for upholding the primacy of these texts.

Muslim scholars, he notes, often refer to the notion of ijtighad (critical and renewed reading of the foundational texts) as the only way for Muslims to take up modern challenges.

But Prof Ramadan argues that, in practice, such readings have reached the limits of their ability to serve the faithful.

In his book, he sets forward a new radical concept of ijtihad, which puts context, including knowledge derived from humans sciences, cultures and historical contingencies, on an equal footing with the scriptures as a source of Islamic Law.

“Muslims have to reform the way they look at themselves, their history and the texts,” he said. “You have to reconcile yourself with yourself.”

He returns to his call for a moratorium on stoning adulterers and on capital punishment, which angered some Muslims and liberals in the west, who criticised him for refusing to confront barbarity and denounce such practices on the grounds that it was Sharia law.

His response was that his position did not count, he was interested in “the evolution in Muslim mentalities”.

He remains convinced that women and the poor remain “the first victims of the literal and often hasty implementation of the texts”.

As for the moratorium, it was no clever trick that played on words.

He writes: “My position defended the idea that whatever the number of poor people or women who were executed, physically punished, or stoned in the world, a moratorium needed to be decided on, to end the implementation of penalties that today represent complete injustice.”

As he headed for Oxford’s High Street in search of a taxi, it struck me just how thankless is his journey, when so many question his sincerity and many more see him as the man to save the world from the clash of civilisations.

It would be tragic indeed, if his message of hope were to become part of the problem.