Members of the House of Commons were sworn in this week as the new Parliament started. As is true in the U.S., members can choose to swear by God that they will bear true allegiance (to Her Majesty there, to the Constitution here), or they can solemnly affirm that they will do the same. But what's interesting is that, as can be seen in the video, in Britain many members actually choose the "affirm" option. The new Conservative Prime Minister, David Cameron, swore, but his Deputy Prime Minister, Liberal Democrat Nick Clegg, affirmed, as did the Speaker and the Leader of the Labour party. Most of the Labour party affirmed; most of the Conservatives swore.
What would happen to a politician in the U.S. today who declined to take an oath and swear by God to support the Constitution? Our Constitution gives the affirm option and provides that "no religious test" shall ever be required for public office, but I think the voters might visit their displeasure on a politician who didn't swear. Apparently Franklin Pierce chose to affirm back in 1853, and Quakers often affirm because their religion takes literally the biblical prohibition on swearing by God. But a politician today who affirmed and explained doing so on the ground that he didn't believe in God would be in some trouble here, I think.