It's an extract from his new memoir, No Laughing Matter.
My major contribution to what, rather pompously, might be called ‘The Concept of Sergeant’ (and, to a great degree, the others of mine) was very simple: Sergeant Grimshawe (the ageless William Hartnell) is about to retire. He has never trained a No. 1 Squad. He’s passionately devoted to mould one aided by Corporal Copping (the rock-solid Bill Owen) out of his last intake. Alas, these National Service conscripts prove to be the Original Awkward Squad - unwilling, uninterested and unlikely to grant him his dream. But, when they hear that Old Leatherlungs has bet his fellow NCOs £50 that he can turn this bunch of dedicated civilians into a unit that even the legendary Guards Regiments would respect, the new soldiers consider: “Grimshawe shouts. Well, that’s what sergeants do. But when has he ever done any of us actual harm? Never.” And so they decide, without fuss, to help him show his fellows he can do it, as well as demonstrate to him that they’re not such a gang of incorrigible misfits after all.
This set the style, to a great extent, of the ones I wrote: the incompetent, the uninterested or the plain unlucky, seen at their worst for most of the story, but triumphing in the end, against all expectation, and to rousing effect, in hospital, school, police force, cruise ship and Helping Hands Agency.