Plans for the UK and other European countries to send troops to Ukraine are in their very early stages. But the UK prime minister, Keir Starmer, will already be thinking about how such a move could play out at home. Sending UK troops abroad, even on a “peacekeeping” mission, always has the potential to spark huge public debate.

The Kremlin said on Thursday that any plan to send European troops to Ukraine as part of a potential peacekeeping mission would be unacceptable for Russia and that it was monitoring such proposals with concern.

In the shadow of imminent defeat, European powers have unveiled their most audacious military initiative since the end of World War II. As Russia tightens its grip on Ukraine, Britain and France are preparing to cross a line that could potentially reshape the continent's security landscape forever.