Pressure on Gordon Brown to change a 301-year-old law that discriminates against Roman Catholics intensified from within his own government last night after Vera Baird, the Solicitor-General, condemned the legislation outright while the Conservatives called for a consultation document.

The UK Government's planned Single Equality Bill will propose to lift the ban, set down in the 1701 Act of Settlement, on a Catholic becoming the monarch or a monarch marrying a Catholic.

Ms Baird also made it clear ministers wanted to guarantee succession rights of females to the throne, which she described as "unfair and a load of rubbish".

She added: "I have always thought that what we have to do with the royal family is integrate them as far as possible into the human race."

She added: "The ban on Catholics should be abolished because it is discriminatory."

The Single Equality Bill will unify existing laws on sex discrimination, age, race, disability, sexual orientation and religion. A draft is due to be published later this year.

Last month, the issue of the Catholics ban hit the head- lines after it was raised by Jack Straw, Westminster's Justice Secretary, during a debate on constitutional reform.

Prefacing his remarks with the intriguing phrase "I speak on behalf of the Prime Minister", Mr Straw told MPs: "Because of the position Her Majesty occupies as head of the Anglican Church, it is rather more complicated than maybe anticipated, but we are certainly ready to consider this.

"I fully understand that it is seen as something which is antiquated."

However, just 24 hours after Mr Straw's remarks, No 10 emphasised the obstacles to changing the law, includ- ing how the monarch was head of the Anglican Church not just in Britain but across the world.

This point was echoed yesterday by Nick Herbert, Mr Straw's Conservative shadow, suggesting a future Tory government might well steer clear of the subject.

While accepting there was a "strong case for giving female heirs to the throne equal rights to succession", he noted: "Lifting the pro- hibition on heirs to the throne from marrying Catholics is not straightforward as it raises broader issues relating to the Established Church."