David Cameron is going to fight a duel. This was much the most interesting thing said by Ed Miliband during Prime Minister’s Questions. The Labour leader unexpectedly announced, while continuing last week’s attack on the Prime Minister about waiting times in Accident and Emergency departments: “Within 24 hours the House of Commons Library had called him out.”

To call someone out is to challenge him or her to a duel. The last Prime Minister to fight a duel was the Duke of Wellington. But he did not take on a librarian. His opponent was the Earl of Winchilsea.

The Duke was heavily criticised in the press for fighting this duel, and one could not help fearing Mr Cameron might also attract a certain amount of adverse comment. What, for example, if the librarian turned out to be a woman? Mr Cameron’s belief in equality would not allow him to back out merely because his opponent happened to be of a different sex.

But it would not look good if having wounded his adversary at dawn behind the bushes in St James’s Park, he drove her to the nearest Accident and Emergency department, only to find she had to wait four hours on a trolley before being treated. Such an anecdote, though of limited statistical value, would tend to support Mr Miliband’s claim that waiting times have got longer.

These thoughts were brought to an end by a member of the columnar research staff, who had discovered a North American meaning of the expression “to call someone out”. Over there, it apparently means, according to the Oxford Dictionaries website, “Draw critical attention to someone’s unacceptable actions or behaviour”.

And this, one fears, must have been the sense in which Mr Miliband was employing it. He is just the sort of person to use a North Americanism. We struggled to come to terms with the realisation that the only duel we would be seeing was the one between Mr Cameron and Mr Miliband.

Each week, the Leader of the Opposition is allowed the choice of weapons. This week he yet again opted to fire some statistics at Mr Cameron, who responded by firing some different statistics back.

Both men missed, but once the fog of numbers had cleared, the Prime Minister was seen to be still standing, entirely unwounded, which we are inclined to think means he had won.

In this safety-conscious age, opportunities for genuine political conflict are becoming ever harder to find. The Prime Minister announced that he intends to reduce them still further, by making proposals in the Conservative manifesto for thresholds in strike ballots. He observed in an indignant tone that tomorrow’s strike by teachers is “going to disrupt our children’s education”.

Nobody ventured to point out that our children might quite like having their education disrupted.