On 13 November, France was struck at its very heart. These terrorist actions were the bloodiest and most horrifying attacks France has experienced in more than half a century.

They caused hundreds of casualties, including one British citizen, brought devastation to their loved ones and outraged millions of people throughout France, Europe and the world, bound together in a movement of shared solidarity that was heart-warming to all French people in these terrible times.

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We were struck, and moved, by reactions in the United Kingdom, both official and unofficial. Spontaneously, British citizens gathered to observe moments of silence and remembrance. People from every neighbourhood in London came to our embassy to demonstrate their solidarity with the French people. And we will never forget hearing the Marseillaise sung by thousands of English football supporters at Wembley.

These gestures of compassion are not only driven by emotion, they are also rooted in the genuine conviction that the enemy of France is also the enemy of the UK.

As David Cameron declared: “Our people stand together, as they have done so many times throughout history when faced with evil. And once again – together – we will prevail.”

This is of particular relevance as France and the UK have recently celebrated the fifth anniversary of the Lancaster House treaty. It is a historic commitment to building a long-term partnership in defence and security.

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With this treaty, France and the UK have now reached a momentous level of mutual trust. Michael Fallon and I have met some 10 times this year alone: there is no important decision we have made in security matters without previously consulting each other.

The Lancaster House treaty reflects our common history, interests, values, responsibilities and understanding of the threats we face. It is the living embodiment of the assertion that there can be no threat to one of our countries that is not a threat to the other. Finally, it is a promise that France and the UK will continue tackling their shared security challenges shoulder to shoulder.

The UK and France have always made decisive contributions to international security. Since the second world war, they have dedicated a substantial share of their national wealth to defence, reflecting the fact that they take their responsibilities as permanent members of the United Nations security council very seriously.

In a context of austerity, both our states made the decision to raise their defence budgets. The British government has made courageous decisions in its strategic defence and security review (SDSR), which we warmly welcome.

We have also achieved a great deal together. We led the international coalition to protect innocent civilians in Libya in 2011. We operated together against the Taliban in Afghanistan and we remain engaged side by side against Isis in Iraq.

Just like France, the UK is working to defeat Isis, training local forces, striking targets in Iraq and providing vital intelligence support. Over Syria, British aircraft are supporting the coalition with intelligence, surveillance and reconnaissance.

Isis is not just present in Iraq. It operates across the border in Syria, where its headquarters are located, in Raqqa. It is from Raqqa that some of the main threats against other countries are planned and orchestrated. That’s why it is now crucial to strike Isis in Syria in order to degrade and, ultimately, to destroy it.

Today, for the very first time since the beginning of the Syrian conflict, diplomatic efforts seem to be converging in Vienna. Western countries, Russia, Iran, Turkey and the Gulf states have agreed to combine their efforts against the threat posed by Isis. We have to jointly seize this opportunity to broaden the coalition that is needed to defeat Isis.

The departure of Bashar al-Assad is essential in order to bring peace to Syria and ensure justice for the hundreds of thousands of men, women and children he has tortured and killed in the worst humanitarian crisis for decades, but it is not a prerequisite for military action against Isis.

Moreover, we need British defence capabilities to win this war. The Royal Air Force is already in action over Iraq. Its involvement over Syria would make a practical difference. The RAF has significant capabilities for precision airstrikes, aerial reconnaissance and air-to-air refuelling support. On a daily basis, its Tornado aircraft and unmanned drones are causing very severe damage to Isis in Iraq. The use of these capabilities over Syria would put additional and extreme pressure on the Isis terror network.

As the SDSR has just been released, providing the UK with the strategy and all the necessary means to cope with its security responsibilities, David Cameron, may – in the coming days – call on the House of Commons to vote in favour of an extension of British strikes to Syria.

It is France’s hope that British forces will soon be working side by side with their French counterparts to take this fight to the very heart of Isis, defeating it and making our countries and peoples safer.