The Pope faces a wave of demonstrations over his planned visit to Britain in the wake of his condemnation of Labour's equality laws.
Humanists, gay groups and academics last night joined politicians in criticising the Pontiff 's unprecedented intervention in domestic politics.
The row will ramp up fears of angry protests greeting Benedict XVI when he arrives in the UK on a date - yet to be confirmed - later this year.
In a lecture to English Roman Catholic bishops in Rome on Sunday, the Pope described Harriet Harman's Equality Bill as 'unjust', restricting religious freedom and violating 'the natural law' - in other words, Christian teaching.
Historians said it was the first direct intervention in British politics by a Pontiff in 300 years.
For centuries, Popes have avoided any comments on domestic politics to free British Catholics from the smear that they are loyal to a foreign power.
The National Secular Society yesterday signalled it would organise protests among gay groups, feminists, pro-abortion campaigners and victims of sexual abuse by priests.
Its president Terry Sanderson said: 'The taxpayer in this country is going to be hit with a bill of some £20million for the visit of the Pope.
'He has already indicated that he will attack equal rights and promote discrimination.'
Prominent gay rights campaigner Peter Tatchell said: 'The Pope's criticism is a coded attack on the legal rights granted to women and gay people.