The Pope confirmed yesterday that he will make an official state visit to Britain this September – and immediately launched an attack on the Government’s plans to introduce stronger equality legislation for gay men and women.

In the first official announcement from the Vatican that the head of the Roman Catholic Church will tour Britain, Pope Benedict XVI called on his bishops to continue campaigning against the Equality Bill which he said threatened religious freedom.

His comments attracted anger from gay rights groups and secularists, who have now promised to protest throughout the pontiff’s visit.

In a letter to the Catholic bishops of England and Wales, many of whom are currently in Rome on an “ad limina” visit, Pope Benedict publicly criticised Britain’s equality legislation for the first time.

“Your country is well known for its firm commitment to equality of opportunity for all members of society,” he wrote. “Yet as you have rightly pointed out, the effect of some of the legislation designed to achieve this goal has been to impose unjust limitations on the freedom of religious communities to act in accordance with their beliefs.

“In some respects it actually violates the natural law upon which the equality of all human beings is grounded and by which it is guaranteed.” In a separate warning to any bishop thinking of deviating from the Vatican’s lead on such controversial issues, Pope Benedict also reiterated the need for the Church to “speak with a united voice”.

“In a social milieu that encourages the expression of a variety of opinions on every question that arises, it is important to recognise dissent for what it is, and not to mistake it for a mature contribution to a balanced and wide-ranging debate,” he said. “It is the truth revealed through scripture and tradition and articulated by the Church’s Magisterium that sets us free.”

The Pope’s comments were a clear assault on the Equality Bill, which consolidates the past 40 years of equality legislation and aims to expand rules stopping employers from discriminating against gay employees because of their sexuality. Churches and religious organisations are currently exempt from the legislation, an exemption the Pope believes his bishops must make sure they maintain.

Last week, an amendment to the Bill which would have more clearly defined which jobs could continue to discriminate against homosexuals was defeated in the House of Lords with help from the Anglican bishops who are also exposed to any expansion of the equality legislation.

Yesterday, the National Secular Society (NSS) said it would try to mobilise a broad protest movement against the Pope’s visit which would include secularists, gay groups, family planning organisations, pro-abortion groups and “anyone who feels under siege from the Vatican’s current militancy”.

They also criticised the estimated £20m cost to the taxpayer that a state visit to Britain – the first by any Pope – would inevitably entail. “If the Catholic Church wishes its leader to come here, it should pay for the visit itself,” said Terry Sanderson, president of the NSS.

The veteran gay rights activist Peter Tatchell said his group Outrage! would protest throughout the Pope’s visit. “The Pope’s criticism that British equality legislation ‘violates the natural law’ is a coded attack on the legal rights granted to women and gay people,” he said.