David Miliband is expected to warn that if Britain leaves the EU it would be disastrous not just for the UK but the rest of the world as he wades into the Brexit debate today.
The former foreign secretary will make a brief foray back into British politics as he delivers a speech urging that Britain stay in the EU as a departure could contribute to the "destruction" of the international order.
Pro-exit Conservative employment minister Priti Patel has already reacted to Miliband's expected warnings by stating he has always been "wrong" on the EU.
Miliband, brother of former Labour leader Ed Miliband, will be speaking in a personal capacity when he delivers a key speech in Westminster later in which he is set to urge "remain" campaigners not to "cede passion or patriotism to the other side" and to continue to fight to stay in the EU.
He will say: "Quitting Europe means giving up on our alliances, forsaking our position at the negotiating table, abandoning our international responsibilities and risks setting off a domino effect that strengthens our enemies and undermines our allies.
"The question of Britain's place in Europe, is not only one of what we 'get' out of Europe. It is also a question of whether we want to shore up the international order, or contribute to its dilution and perhaps even destruction.
"My point is that this is not just bad for Britain. It is very bad for the international order, and the aspirations for that order, on which we depend."