Islam is stuck in its own version of the “Middle Ages” which is contributing to a global crisis, one of the religion's leading experts has argued.

Professor Hans Kung, a leading Roman Catholic and theologian from Germany, warned in a lecture of a “deadly threat” to all humankind unless new efforts are made to build bridges with Islam.

He said in London that Islam has “special problems” with modernity because, unike Christianity and Judaism, in which he also specialises, it has never undergone a “serious religious reformation”.

He questioned whether Islam is even capable of adapting to a post-modern world in the way that Christianity and Judaism have done. But he also outlined why he is hopeful that the present problems around radicalisation within Islam can be resolved, and how the other two Abrahamic faiths are subject to some of the same problems on their extremist edges.

Violence has been practicised in the sign of the crescent, but also in the sign of the cross, he warned.

In his lecture, seen by The Times, Professor Kung said: “The options have become clear: either rivalry of the religions, clash of civilizations, war of the nations - or dialogue of civilizations and peace between the nations as a presupposition for peace between the nations.

“In the face of the deadly threat to all humankind, instead of building new dams of hatred, revenge and enmity, we should tear down the walls of prejudice stone by stone and thus build bridges of dialogue, bridges particularly towards Islam.”

Professor Kung, author of Islam: Past, Present and Future, published last year and one of the most authoritative works on the subject, was speaking on “Challenges to Islam, Christianity and Judaism” in a lecture organised by the Royal Fine Art Commission Trust and Sky Arts. It will be broadcast on Sky Arts later this month.

He described how liberal Jews, Christians and Muslims often get on better with each other than they do with fellow Jews, Christians and Muslims from the traditionalist wings of those religions. A Roman Catholic “imprisoned in the Middle Ages” will find himself closer to the “medieval element” of Islam and Judaism than with liberal Catholic believers.

Professor Kung said that one of the main causes of conflicts between religions is the persistence of outdated ways of thinking.

Islam and Christianity regard the actual Middle Ages as the “great time” for their religions. But modernity has forced all three religions of the book onto the “defensive”, and they all face challenges over how they react to their own “Middle Ages”.

He argued that Christianity and Judaism have moved on, but not Islam, adding: “It remains an open question if the ecumenical paradigm of post-modernity will develop also in Islam.” Professor Kung, who aged 80 is a contemporary of the Pope and worked with him as a theological adviser to the Second Vatican Council in the early 1960s, was influential at the council in persuading the Roman Catholic Church to adopt a more positive attitude to Judaism and religious freedom.

He has also spoken out constantly in favour of the official recognition of the State of Israel by the Vatican and for a two-state-solution for Israelis and Palestinians.

Professor Kung, whose own liberal views cost him his official Catholic teaching licence in the last century, said that the essence of all three religions must be preserved, but those who want peace and reconciliation will not be able to avoid criticism. They must engage in self-criticism to enable their faiths to adapt to modernity.

Referring to Christianity, for example, he said: “Jesus Christ as a basic model is a constant, but the law of celibacy is a variable.”

He argued: “After the Reformation, Christianity had to undergo another paradigm shift, that of the Enlightenment. Judaism, after the French Revolution and Napoleon, experienced the Enlightenment first, and as a consequence, at least in Reform Judaism, it experienced also a religious reformation. Islam, however, has not undergone a serious religious reformation and so to the present day has quite special problems also with modernity and its core components, freedom of conscience and religion, human rights, tolerance, democracy."

Professor Kung also set out what the three religions have in common, such as injunctions against murder and respect for life. “They do not recognise themselves in our picture of Islam, because they want to be loyal citizens of the Islamic religion.

"Those who make Islam responsible for kidnappings, suicide attacks, car bombs and beheadings carried out by a few blind extremists ought at the same time to condemn Christianity or Judaism for the barbarous maltreatment of prisoners, the air strikes and tank attacks carried out by the US Army - 10,000 civilians have been murdered in Iraq alone - and the terrorism of the Israeli army in Palestine.”

Professor Kung’s lecture will be broadcast on Sky Arts, channel 267, on June 23 at 7.15pm The Sky Arts accompanying series on the art and architecture of religious buildings, called Art of Faith, can be seen on Sunday nights at 7pm.