In this photo illustration, the European Union and the Union flag sit together on March 17, 2016, in Knutsford, United Kingdom. christopher furlong/getty images

“If we leave, the only certainty we’ll have is uncertainty,” British Prime Minister David Cameron said in a speech in London Monday, warning that if the U.K. leaves the European Union, it would increase the risk of Europe descending into war.

“The European Union has helped reconcile countries which were at each others’ throats for decades,” Cameron said. “Britain has a fundamental national interest in maintaining common purpose in Europe to avoid future conflict between European countries.”

With only six weeks to go until the June 23 referendum on the so-called Brexit, both the “Leave” and the “Remain” campaigns have ramped up their rhetoric. In his speech, Cameron focused on what he called a “big, bold patriotic case,” to remain in the EU, even invoking Winston Churchill’s “lone stand” against Nazi Germany in 1940.

“From Caesar’s legions to the wars of the Spanish succession, from the Napoleonic wars to the fall of the Berlin Wall. Proud as we are of our global reach and our global connections, Britain has also always been a European power, and we always will be,” Cameron said. “Can we be so sure that peace and stability on our continent are assured beyond any shadow of doubt? Is that a risk worth taking? I would never be so rash as to make that assumption.”

“The truth is this — what happens in our neighborhood matters to Britain. That was true in 1914, in 1940 and in 1989. ... And if things go wrong in Europe, let’s not pretend we can be immune from the consequences,” he added, referring to the two World Wars and the fall of the Berlin Wall.

Cameron’s comments come just a day after the British Chancellor of the Exchequer George Osborne — who has previously said that a vote to leave the 28-nation bloc would be the “most extraordinary self-inflicted wound” — warned that Brexit would be “catastrophic for peoples’ jobs and their incomes and their livelihoods.”

“You will see the analysis we will do, but I’m pretty clear that there will be a significant hit to the value of people’s homes and to the costs of mortgages. That is one example of the kind of impact, economic impact, that we get from leaving the EU,” Osborne said in an interview with ITV. “Now, some people might think wrecking the economy is a price worth paying. I absolutely reject that.”

Osborne’s comments came in response to Justice Secretary Michael Gove’s assertion that the U.K. could leave the EU’s single market without damaging trade.

Later on Monday, former London mayor Boris Johnson — a prominent campaigner for the Leave side — is also due to give a speech, during which he is expected to make a “cosmopolitan case for Brexit.”