Watching the extraordinary scenes in the House of Commons yesterday after the impressive Speaker forced the PM in to emergency questions over the Hunt affair, two quotations did actually come to me – for once.

The first is Goethe's: "There is nothing in which people more betray their character than in what they laugh at." The second, Abraham Lincoln's: "Nearly all men can stand adversity, but if you want to test a man's character, give him power."

David Cameron's line to Dennis Skinner, 81, reveals more about him than its intended victim. His reply to "the Beast of Bolsover's" suggestion that Mr Cameron was keeping Mr Hunt in his job to "prevent bullets hitting the PM" was dismissive: "Well, the honourable gentleman has the right, at any time, to take his pension and I advise him to do so."

Mr Skinner has delivered many a caustic barb over his 42-year career as an MP. Most recently, his "when posh boys are in trouble, they sack the servants" jibe at Mr Hunt for keeping his job while special adviser Adam Smith took a fall went viral. That's what backbench MPs do.

What Prime Ministers do not, or should not, do is insult one of the more senior members of the House on the grounds of age. Certainly not a senior member who does not miss a sitting, believing it is every MP's duty to be there, every day.

Two days before local elections, how does this play to older voters from a PM already in trouble with women because of outbursts like "calm down, dear" to a female MP? The PM has long been regarded as the Tories' best asset. Now the heat is on and the strain is truly showing. His insult will wash over the thick-skinned Dennis, but such casual ageism reflects badly on the PM, and reinforces a "nasty party" image he has battled so hard to dispel.