According to Westminster tradition, a British prime minister should announce big policy changes on the floor of the House of Commons, rather than via press conference or backhand media briefing. But it’s also a Westminster tradition that every British prime minister almost entirely ignores this custom.

So it was a genuine surprise when Keir Starmer stood up in parliament on Tuesday and really did spring a major announcement: a £6 billion ($12 billion) boost to annual defence spending, controversially funded by a near-equivalent cut in Britain’s foreign aid budget, which takes UK military munificence to 2.5 per cent of GDP by 2027.