Labour MP Dan Jarvis is to warn that Brexit will be 'a gift' to Russian President Vladimir Putin and others who want to weaken Europe's defences.
In his first major speech of the EU referendum campaign, the former Paratrooper and shadow foreign minister will say on Wednesday that the poll on June 23 is “the moment to decide whether we want to be Great or little Britain”.
Speaking at the Poppy Club in London, the Barnsley Central MP - seen by some of his colleagues as a future Labour leader - will outline why Britain’s security and global influence are best served by remaining in the European Union.
Jarvis will highlight how the networks provided by the EU helps combat terrorism, how the EU helps project Britain’s influence in the world and how the EU supports jobs in Britain’s world-leading defence and security industry.
At the event, he will also be joined by actor Ross Kemp, who will also announce his public backing for the Remain campaign in the upcoming referendum.
Jarvis - who served in Afghanistan and Iraq, as well as in Kosovo - will say: "Britain leaving the EU would undermine vital efforts for peace and stability. And rather than security it would lead to uncertainty.
"We are being asked to gamble on a profound and permanent break from a partnership which has secured peace and promotes cooperation to deal with emerging threats.
"What sort of message would we send out to the rest of the world, and to our enemies, if we, the people who forged cooperation across borders, who enlarged and later led this partnership between nations, walked away?
"It would be a gift to Putin, weakening both NATO and the EU.”
Senior former military chiefs have already warned that Brexit would undermine the EU's tough line on sanctions against Russia after its military action in Ukraine.
Speaking to HuffPost UK last year, Jarvis talked about his experiences in Kosovo and Iraq.
Jarvis will add: “This referendum is the moment to decide whether we want to be Great or little Britain.
"On the 23rd June we face a choice between greater security and global influence as part of the EU or a period of prolonged uncertainty and permanent retrenchment by walking away.
"For the Leave campaign to assert that both everything will change, but nothing will change is not simply a contradiction. It fails in our collective duty to serve the national interest.
"This matters because while this is a decision for us today, it is a decision from which there is no going back."