He said: “When a body loses its sense of direction and is no longer able to look ahead, it experiences a regression and, in the long run, risks dying.” The Pope went on to condemn anti-immigrant populism and extremism, which he said posed a “mortal threat” to the union.

Prime ministers and presidents from 27 EU members states have gathered in Italy to mark the 1957 founding of the Treaty of Rome, receiving a Papal blessing on the eve of the anniversary. Celebrations around the milestone have been muted by unease within the bloc, mainly due to a number of prolonged economic crises and an unresolved migrant situation. Prime Minister Theresa May did not attend the meeting of leaders at the Vatican.

The addition of Brexit has caused extra strain on relations, with Britain due to trigger Article 50 within days, marking the beginning of divorce proceedings with the EU. The Argentinian-born pontiff told the leaders they needed to promote Europe's "patrimony of ideals and spiritual values" with greater passion and vigour.

"For it is the best antidote against the vacuum of values of our time, which provides a fertile terrain for every form of extremism," he said, mentioning the attack in London this week by a British-born convert to Islam, who killed four people. The pope has repeatedly criticised Europe over the past five years for its perceived lack of vision, drawing the ire of German Chancellor Angela Merkel in 2014 when he described the EU as an elderly woman who was "no longer fertile and vibrant".