The two men discussed Iraq, the Middle East and the EU, a Vatican statement said, making no mention of a change of faith for Blair. Cherie Blair, who is Catholic, accompanied her husband. She greeted the pope after her husband's 20-minute meeting.

There has been speculation that Blair, an Anglican, is planning to convert.

The pope and Blair were joined after their talks by Cardinal Cormac Murphy-O'Connor, archbishop of Westminster and the head of the Catholic church in England and Wales.

The Blairs gave the pope a frame containing three period photographs of a famous British convert to Catholicism, Cardinal John Henry Newman, who died in 1890.

Cardinal Newman converted in 1845 and was later made a cardinal of the Catholic Church.

In 1991 he was declared 'venerable', putting him on the road to Catholic sainthood.

After the pope welcomed Blair into the study, the prime minister told him he had just flown in from the EU summit in Brussels where European leaders reached agreement on a deal to overhaul the 27-nation bloc.

"I heard it was very successful, " the pope told Blair. "Yes, but it was a very long night. We finished up at 5.30 in the morning, " Blair said.

Speaking before his private audience with the pope, he said the issue of his conversion to Catholicism was "unresolved".

Asked if he would be converting, he said: "Things aren't always as resolved as they might be". He said he was "nervous" discussing the issue before yesterday's meeting.

Blair's audience with the pope was the final foreign engagement of his 'farewell tour'. He is set to leave Downing Street on Wednesday.

Blair said about the subject of conversion: "I don't want to talk about it. It's difficult with some of these things".

There is no constitutional barrier to such a conversion, which would have made Blair Britain's first Catholic prime minister.

However, it has been suggested he would wait until after leaving office to avoid possible clashes such as over his role in appointing Church of England bishops.

Downing Street said before the meeting that Blair wanted to discuss "interfaith issues" with the pope.