Gordon Brown supports reform of laws linked to the monarchy
Gordon Brown apparently believes that the ancient law which bars British monarchs from marrying Catholics is an anachronism in the 21st Century. He supports reform of this and associated laws.
But the DUP's Jeffrey Donaldson has warned the government against "tinkering" with a law that "protects the constitutional position of the country". He suggested it was a question of allegiance, because Catholics were bound to put Pope before patriotic duty.
Alasdair McDonnell, of the SDLP, has dismissed Mr Donaldson's argument as being based on "poisonous 16th century propaganda".
The issue is raised as a result of a Private Members' Bill at Westminster introduced by Liberal Democrat Evan Harris. His bill would allow the British monarch to marry a Catholic and end male primogeniture - the principle that men are privileged over their sisters in the line of succession.
The bill is doomed to fail.
But Downing Street has indicated that it supports its core principles and has already been in discussion with Buckingham Palace about the same issues. Any changes would also require support from the 53 Commonwealth countries.
Certainly in an era of human rights and equal opportunity it's hard, on a point of principle at least, to defend legislation that clearly discriminates against Catholics and women.
Jeffrey Donaldson makes a stab at defending it on a practical level by suggesting that any changes would profoundly alter the constitutional position of the country - a constitution where, ironically somewhat like Catholic dogma, tradition is vitally important.
He uses terms like "tamper" and "unpick" to describe the government's approach to this - thereby suggesting that any changes will not be fully thought through and could be more far-reaching than intended.
Or perhaps the changes are just more far-reaching than the government would care to admit.
Tony Blair shied away from tackling this issue.
His own journey towards Catholicism was probably a factor because any initiative of his could have been characterised as a papist plot.
Gordon Brown, as the son of the manse, is on stronger ground.
The fact is, reforming the Act of Settlement from a principled position would necessarily go further than Mr Harris's bill. It would not bear scrutiny to end the ban on marrying Catholics for discriminatory reasons, but continue to maintain a ban on the monarch themselves being Catholic.
An article in The Guardian last September suggested that Downing Street had already drawn up plans to end the exclusion of Catholics from the throne and planned to introduce such legislation quickly in a fourth term.
So, any change hinges on a Labour victory? Not necessarily, because there are strong advocates of change on the Conservative benches too.
The problem, as Jeffrey Donaldson identifies, is the domino effect of any change. The head of state might no longer be able to be head of the Church of England and the church would become disestablished.
And if the overriding principle is ending discrimination, then the next stage - according to the constitutional lawyer Geoffrey Robertson QC - is for the government to challenge the notion of a head of state being selected through inheritance.
At that point the United Kingdom becomes the United Republic.
We may get a chance to discuss some of this on The Politics Show this Sunday with Arlene Foster, Sir Reg Empey and Alasdair McDonnell.
We'll also report on the plight of the neglected west - Robin has more on that on our website - and we find out why climate change is a sectarian issue.
See you Sunday
PS - At a discussion I hosted this week with politicians and young volunteers, the big issue of alcohol and its control was raised. A teenage member of the panel suggested the legal age for purchasing alcohol be changed. Politicians nodded in agreement until the young contributor suggested the appropriate age - 12.