David Cameron used the iconic backdrop of the British Museum to argue that the UK is "stronger, safer and better off" inside the EU, with just over a month to go before the 23 June ballot. The prime minister evoked war leader Sir Winston Churchill and Britain's lone stand against Nazi Germany in 1940 to argue the case for a united Europe.
"It wasn't through choice that we were alone. Churchill never wanted that. Indeed he spent the months before the Battle of Britain began trying to keep our French allies in the war, and then after France fell, he spent the next 18 months persuading the United States to come to our aid," Cameron declared.
The Conservative leader also claimed that the EU is a "vital reinforcement" to Nato in keeping peace on the continent as well as countering terrorist plots on the British mainland.
"The threat has not only grown, it has changed in its nature. The attacks in Paris and Brussels are a reminder that we face these threats together and will only succeed in overcoming it by working much more closely together. These terrorists operate throughout Europe," the prime minister said.
"Their networks use technology to spread their poison and to organise beyond geographical limits. People say to keep our defences up you need a border and their right. That's why we kept our borders and we can check any passport, including for EU nationals, and we retain control of who we allow in to our country.
"But against the modern threat, having a border isn't enough. You also need information, you need data, you need intelligence, you need to cooperate with others to create mechanisms for sharing this information."
Cameron admitted that a Brexit would not prevent the UK securing bilateral intelligence sharing deals with EU nations, but warned breaking away from Brussels would make it slower and harder for the security services to cooperate with their colleagues on the continent.
"The EU is not some peripheral institution, or a hindrance we have to work around it is now an absolutely essential to how Britain can get things done," the prime minister added.
"Not by creating some vast EU bureaucracy, nor by sucking away the role and capabilities of our own world-beating intelligence and law enforcement agencies, but because their superb work depends on much closer co-operation between European governments and much faster and determined action across Europe to deal with this new threat."
'EU creates hostility'
But Ukip leader Nigel Farage attempted to rebut Cameron's security claims by arguing that the EU had increased hostility on the continent. "Far from being a cause of peace, the European Union has increased hostility in Europe," the Brexit campaigner said.
"Ultimately it is a lack of democracy that leads to war and conflict. The EU's crushing of democracy in Greece has led to the rise of extreme parties such as Golden Dawn.
"The anti-democratic EU, far from bringing countries together, has divided Europe. As they continue to drive through the failed Euro single currency project, it is the lives of ordinary citizens across Europe who suffer at the hands of the EU nationalists who refuse to contemplate anything than deeper, total and complete EU integration."
The prime minister's address came hours before Boris Johnson, his chief Conservative rival, is expected to make a major address on the issue. The former Mayor of London will make the "liberal, cosmopolitan case" for a "leave" vote.