Pope Benedict XVI has attacked the "increasing marginalisation" of Christianity, arguing that religion should be recognised for its "vital" contribution to the nation.

The Pontiff told MPs, peers, and religious leaders in Westminster Hall that there were "worrying signs" of a failure to appreciate the rights of believers to freedom of conscience and the "legitimate" role of religion in public life.

In his speech, the Pope said he was voicing his concern at the growing marginalisation of religion - particularly of Christianity - even in nations which place a great emphasis on tolerance.

"There are those who would advocate that the voice of religion be silenced, or least relegated to the purely private sphere," he said.

"There are those who argue that the public celebration of festivals such as Christmas should be discouraged, in the questionable belief that it might somehow offend those of other religions or none.

"And there are those who argue - paradoxically, with the intention of eliminating discrimination - that Christians in public roles should be required at times to act against their conscience."

The Pope's remarks are likely to be interpreted as aimed in part at the failure of the Catholic adoption agencies to retain the right to refuse gay couples as potential adoptive parents.

Former prime ministers Tony Blair, Gordon Brown, Sir John Major and Baroness Thatcher were all present in Westminster Hall to hear the speech.