The Reverend Ian Paisley must be going an even redder shade of puce. The Roman Catholic Church is, after all, The Abomination of the Earth and the Scarlet Whore of Babylon. How, then, will he reconcile himself to the news that the Queen – to whom, wearing his political cap, he purports to be "loyal" – has invited a representative of the Anti-Christ in England and Wales to stay with her for the weekend at her Norfolk estate in Sandringham? The theological gloves will have to come off. No more Mr Nice Guy Fawkes.
For 500 years, the English Crown has been the last bastion, apart from neo-Jurassic survivors like Dr Paisley, of the anti-Catholicism which was once deep-rooted in English life. By and large, it has now evaporated. With the election of Iain Duncan Smith, our three main political parties are now led by two-and-a-half Catholics (Mr Blair is nominally an Anglican but is spotted by mass-going regulars at prayer in Westminster's Catholic cathedral two or three times a week).
Yet when a political commentator pointed out this Roman confluence at the top of the nation's party system it created virtually no stir on the political waters. The sign of the cross is now just a sign of the times.
But it takes institutions some time to catch up with cultural change. Particularly where constitutional sensitivities are in play. The Queen is, after all, the Supreme Governor of the Church of England, which is, in ecclesiological terms, just one step down from God.
For her to invite Cardinal Cormac Murphy O'Connor not just to overnight in her cosy 274-room Norfolk mansion but also to preach to her in the estate church is a gesture of goodwill without precedent since Reformation times.
In one sense, of course, Cormac is a safe bet as a house guest. He may not be quite as posh as his predecessor, Basil, but he's a public schoolboy who will be quite at home with all the changing for dinner. (Guests can have to change their outfits as many as five times a day – when Her Majesty switches, you're supposed to too).
And he can be counted on to be more respectful than those junior royals who have apparently been known to alleviate the boredom of lunch with Grandma by running a book on how long the meal will last. (The stopwatch starts when the first course of potted shrimps is placed in front of Her Majesty and ticks until the moment she puts down her cheese knife).
Not that there will be any of that when the Cardinal calls in January. It won't a weekend on which invitations to all junior royals will be de rigueur. The Queen will invite only those private guests she wants and if the invitation was originally intended for the late Cardinal Hume – to whom the monarch once memorably referred as "my cardinal" – she will greet his successor with a warmth that she has been extending to his church for some time.
In 1982, she became the first sovereign for half-a-millennium to invite the Pope to Buckingham Palace. And when, in 1995 she became the first monarch since the Stuarts to take part in a Catholic service, attending vespers at Westminster Cathedral, Cardinal Hume later privately described the event to friends as "the highpoint of my archiepiscopacy".
It went unreported but, at their last meeting, the English Catholic bishops decided to issue an instruction to all parishes to offer a mass of thanksgiving for the Queen's Golden Jubilee next year. Moreover, they have asked that at each service the congregation should sing "God Save the Queen", an anthem that was written in the anti-Catholic fervour of the Jacobite rebellion.
It's a good job that the Dr Paisley won't taint himself by crossing a Catholic threshold to attend one of the services. He might find that the words of the hymn begin to stick in his throat.