The UK Government is working on a detailed plan to change or even scrap the Act of Settlement, which bans Roman Catholics from becoming king or queen and prevents the monarch from marrying a Catholic, The Herald has been told.

In an exclusive interview, Jim Murphy, the Scottish Secretary, revealed how Jack Straw, the Westminster Justice Secretary in overall charge of constitutional matters, is working behind the scenes to change a 307-year-old pillar of the British constitution, which is offensive to many Catholics and non-Catholics, who regard it as unfair and discriminatory.

Speaking for the first time about the matter, the Secretary of State, who is a Catholic, said: "It's wrong to have a settled constitutional position that discriminates . . . I've spoken to Jack about it and he is leading on it. He is putting an awful lot of work into it. He is working hard and is pretty focused on it."

Asked if the UK Government could come forward with a set of proposals to change the law before the next General Election, he replied: "I'd like to see change. It's important we make progress before the next election but the truth is it won't be changed by then."

It could mean that Labour will pledge to change or repeal the law in its election manifesto.

The contentious issue has been raised from time to time but all recent attempts to get the 1701 Act repealed have failed.

In 2001, ex-PM Tony Blair - now a Catholic - promised to re-examine the legislation, but did nothing about it. In March, it was touched upon in the Commons when Mr Straw, stressing he was speaking on behalf of Prime Minister Gordon Brown, made clear the UK Government was "ready to consider" changing the law.

At the time, Jim Devine, the MP for Livingston and one of 13 Scottish Labour MPs who are Catholics, denounced the act as "legalised sectarianism".

Most recently, in November, former home secretary John Reid, also a Catholic, branded the legislation "divisive, discriminatory . . . long outdated and to many people offensive".

Mr Reid added: "If you're going to create a Britain in which we truly have equality, you can't have institutionalised discrimination at the centre of the state. Therefore, we need to repeal or amend those provisions of the Act of Settlement."

Alex Salmond, after becoming First Minister, said he would raise the issue of abolishing the Act of Settlement. One suggestion is that pushing for a repeal would help the SNP woo the Catholic vote in Scotland.

Recent research suggests there are now more active Catholics than Anglicans in Britain, helped by the influx of Polish workers.

Mr Murphy pointed out how changing the act was a "very difficult and intricate problem, but one I want resolved".

It would not only involve the sovereign as Supreme Governor of the Church of England but also the Anglican community across the world; opening up the monarchy to a Catholic could, in theory, lead to the disestablishment of the Church of England. This suggests that work being done by officials and ministers must include liaison with Buckingham Palace.

Prince Charles has let it be known he would like to be "defender of faith" if and when he succeeds to the throne.

Mr Reid, when asked about the heir to the throne and possible constitutional changes, noted: "He is a man who has shown great foresight and inclusiveness in every other area."

However, any proposed changes are likely to run into fierce opposition in some political and religious circles.

In his interview, Mr Murphy recalled how, when he was Europe Minister, he visited Sarajevo, where he met the three-person rotating presidency - a Bosnian, a Serb and a Croat. He was told that a Jew could not be president unless he or she designated themselves as part of one of the three other ethnic groups.

"In the same way that's wrong, the settlement we have in the United Kingdom is unfair. I would like to see it changed. It's not because I'm a Catholic that I feel it. It's unfair, wrong, discriminatory and does not fit well into a modern sense of what Britain is about," he added.

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