David Cameron, Boris Johnson
Cameron and Johnson put on a united front ahead of the 5 May vote, with the prime minister praising Johnson's legacy in City Hall Getty

David Cameron and Boris Johnson will renew their rivalry as the Conservative heavyweights deliver major speeches on the EU referendum on 9 May. The prime minister has warned that there could be another war on the continent if the UK were to break away from the 28-nation-bloc.

"Can we be so sure that peace and stability on our continent are assured beyond any shadow of doubt?" Cameron said, referencing the Ukrainian civil war and conflict in the Balkans. The speech came just days after the Mayor of London election, which saw Labour's Sadiq Khan beat Tory candidate Zac Goldsmith.

Cameron and Johnson put on a united front ahead of the 5 May vote, with the prime minister praising Johnson's legacy in City Hall. But as the EU referendum campaign ramps up, the top Tories will continue to clash as we near the 23 June ballot. Johnson, one of the leading Brexit campaigners, will make the "liberal, cosmopolitan case" for voting "leave" when he delivers his own EU referendum speech after Cameron.

The address will come after two former intelligence chiefs intervened in the debate over the weekend. Sir John Sawers, the former head of MI6, and Lord Jonathan Evans, the former director-general of MI5, backed a "remain" vote and argued Britain would be safer inside the EU.

"It's not just about the day-to-day cooperation, it's about the wider stability of our continent. We are only secure because the wider Europe is secure," Sawers told BBC One's Andrew Marr show.

"Pulling out will make it more dangerous. There is a real risk of the pressures on the EU – migration pressure, economic pressures, pressures from Russia – pulling the EU apart. We are seeing politics in Europe going to the extreme left, to the extreme right."

But Justice Secretary Michael Gove argued the UK would be safer outside the 28-nation-bloc by stopping inference from EU courts in how Britain's security services operate.

"It is dangerous for the European Courts to have a say over our intelligence services and to rule on what data we can share with our allies like the US and Australia," the Vote Leave spokesman said.

"Our intelligence network with the Five Eyes is the cornerstone of our fight against the global terror threat. The EU is jealous of this arrangement and many would like EU structures to replace our international networks.

Gove added: "The home secretary is currently trying to stop EU judges from meddling in these networks but the court case will not be decided until after the referendum. That is something that people need to be aware of before they vote.

"If you vote remain, the EU courts will interfere more with our intelligence agencies, preventing them from fighting effectively against Isis – this makes us less safe. If we Vote Leave, we take back control and stop EU judges from meddling in our affairs."