If Starmer wasn't already a lame duck, you'd be calling this a resignation matter. He's failed to adjudicate a conflict between MOD and HMT by going "I'm the PM and I've staked my reputation on defence: find the money" because he's a coward interpersonally, and politically (ie. won't raise taxes).
Euan Healey
NEW: John Healey quits over defence funding. Devastating letter for the government and Keir Starmer: “You have been unable and the Treasury has been unwilling to commit the resources the nation needs to defend the country at this time of rising threats.”