Who was the bashful boy at the back? D Cameron, Witney, of course

Hurrying into the Commons just in time for the debate on Trident was a fresh-faced Tory backbencher. As he hastened up the aisle, a handful of fellow MPs welcomed him with a little cheer of encouragement. Beaming bashfully, he slid into the seat next to Sir Simon Burns, MP for Chelmsford – an old hand who will be able to offer his younger colleague guidance.

For now, the pink-cheeked rookie contented himself with listening in earnest silence to the Prime Minister, as she began setting out the case for Britain’s nuclear deterrent.

Up in the press gallery, I asked a colleague for the newcomer’s name.

“David Cameron,” he whispered. “MP for Witney in Oxfordshire. Worth keeping an eye on. A lot of Tories have nothing but praise for him. Particularly the ones who campaigned for Brexit.”

The debate opened with Theresa May’s first appearance at the dispatch box as Prime Minister. It was an ideal way to start, given that not only was the Government on her side, but almost all of the Opposition.

Little more than five minutes had passed before a Labour MP (John Woodock, Barrow and Furness) leapt up to denounce the anti-Trident stance of his leader, Jeremy Corbyn. Mrs May welcomed this, and quoted Labour’s official view on Trident, which is firmly pro. British politics in 2016, ladies and gentlemen: a Tory PM approvingly quotes Labour policy, while a Labour leader argues against it.

The SNP, who shared Mr Corbyn’s opposition to Trident, asked Mrs May if she was really prepared “to launch a nuclear strike that could kill a hundred thousand innocent men, women and children?” “Yes,” replied Mrs May, without hesitation.

“Wow!” gasped the SNP benches theatrically, pretending to be shocked – as if they’d expected her to say, “Heavens, no. Our enemies must understand that if they attack us, I would never fire back!”

Mr Corbyn spoke next. It was some spectacle: the Labour leader arguing one way, his MPs disagreeing.

“My honourable friend is very fond of telling us that party conference is sovereign when it comes to policy,” snapped Angela Smith (Lab, Penistone and Stockbridge). “Last year, conference voted overwhelmingly in favour of maintaining the nuclear deterrent!” Other Labour MPs cheered. “Party policy is also to review our policies!” retorted Mr Corbyn, somewhat wildly. Tory MPs laughed.

To be fair to Mr Corbyn: in this case, Labour’s official policy is irrelevant. If their leader is anti-nukes, then effectively their policy is anti-nukes, too. For nuclear weapons to work as a deterrent, the enemy must believe that the prime minister would be prepared to launch them. Mr Corbyn has made it unequivocally clear that he would not, in any circumstances. Therefore, if Mr Corbyn becomes prime minister, Britain will have effectively disarmed, whatever Labour’s manifesto says.

Admittedly, of course, that’s a fairly big “if ”.