VIDEO | Pope returns to Vatican after four day tour of Britain

Before setting off from Birmingham Airport the Pontiff said: "Thank you for the warmth of your welcome and for the hospitality that I have enjoyed.

"The very diversity of modern Britain is a challenge... but it also represents a great opportunity to further intercultural and inter-religious dialogue for the enrichment of the entire community."

The four-day Papal visit has, at times, been an uncomfortable one for the British Government.

He attacked what he called "aggressive secularism" and warned against the "marginalisation" of Christianity in Britain.

But Cameron, in a ceremony before the Pope's flight, thanked him for challenging Britain to "sit up and think".

The PM said: "People do not have to share a religious faith or agree with religion on everything to see the benefit of asking the searching questions that you, your Holiness, have posed to us about our society and how we treat ourselves and treat each other.

"You have really challenged the whole country to sit up and think, and that can only be a good thing."

Cameron added: "When you think of our country, think of it as one that not only cherishes faith, but one that is deeply, but quietly, compassionate."

Earlier, the Pope celebrated a special open-air Mass to put an English cardinal on the path to sainthood - while paying tribute to those who fought the Nazis.

Around 55,000 people attended the ceremony at Cofton Park, Birmingham, on the final day of his four-day visit to the UK.

During the two-hour Mass to beatify 19th Century Cardinal John Henry Newman, he also marked the 70th anniversary of the Battle of Britain.

Pope Benedict XVI paid tribute to those who sacrificed their lives resisting the "evil ideology" of the Nazi regime.

He added: "My thoughts go in particular to nearby Coventry, which suffered such heavy bombardment and massive loss of life in November 1940.

"Seventy years later, we recall with shame and horror the dreadful toll of death and destruction that war brings in its wake, and we renew our resolve to work for peace and reconciliation wherever the threat of conflict looms."

Thousands of cheering pilgrims greeted the Pope in Birmingham and he delighted many of the faithful by personally blessing them and kissing children and babies.

It was the 83-year-old's first beatification since he was elected Pope in 2005.