Once again, Europe has been placed at the mercy of terrorists. Innocent people are dead and injured and others will forever be haunted by the carnage they witnessed. But the wider impact of the terror attack in central London on Wednesday night is only starting to emerge.
This, we now know, was not a crime committed by a radical who grew up in an atmosphere of hate amid the bombs and bullets of a far-away country ripped apart by war. This was a crime committed by a man who lived and worked in our society, who grew up here - and who was radicalised here.
And so all society has a special responsibility to prevent this from happening again. As Europeans, we cannot and should not live this way.
For the most part, Britain is a safe and secure place to live, a gloriously multi-cultural, multi-faith society which celebrates tolerance religious freedom. These values are a way of life, as was vividly demonstrated by the gathering at the candlelit vigil at Trafalgar Square last night.
But despite our nation's solidarity and our ever-increasing security and defence measures, horrific acts of terror are still not being prevented.
So many Europeans have been violently murdered in terrorist attacks, in places like Brussels, Essen, Nice, Munich, Ansbach, Hamberg and Berlin. Europe is in danger. We must warn, ring an alarm bell about the threat, the threat that has come to our common home challenging us every day, every day.
Terrorism has no religion, colour or creed. As we learn that the victims of Wednesday's attack represent at least 12 different nationalities, we must not ask for whom the bell rings. The bell rings for all Europeans.
There has been a constant assault on Europe from those who seek to inflict terror and destruction. Today, we know that there are around 3,000 people on the MI5 list thought to be capable of a terrorist attack. We also know that list is growing daily, and it is likely the atrocity we've witnessed this week will expand recruitment within communities across Europe.
The Jews in Europe are painfully aware of the continuing threat facing Europe. Unlike any other minority, we have been targets of Islamist extremists, as well as the far Right and also the far Left.
We know the value of standing together to fight a common enemy. As responsible Europeans, all society must join forces in defence of our shared values against extremism, radicalism and terrorism.
What can we do to restore ensure peace? Firstly, we must recognise this murderous ideology targets all of Europeans and all of Europe must stand together to fight this scourge. We need greater intelligence sharing among European law enforcement and intelligence agencies and stronger policing laws to act against those in Europe, and across the world, who provide the means, motivation and ideology to enable these attacks.
Across the world, governments are also waking up to the need to engage communities in addressing the root causes of violent extremism. Yet these initiatives account for only a small fraction of the money being spent on military action to target terrorists. History has told us that we cannot rely only on military solutions to combat violent extremism.
The key is to cut it at its roots. This can be done through the promotion of respect and understanding between people in schools, universities, places of worship and neighbourhoods where people meet. Fundamental terrorism is often built out of poverty and social exclusion, and by creating strong social networks alongside educational programmes, we can hope to make it harder for jihadists to exploit and incite people to hatred.
We must also continue to pressure social media networks whose platforms give oxygen to the vile ideologies of extremists. Astonishingly, guides to mounting car terror attacks - manuals that UK jihadists can use for training - were available on Google and Twitter. We can no longer allow social media companies to shirk their responsibilities to remove vile materials that incites terrorism, and we must use legislation and heavy financial penalties - as Germany has proposed - if necessary. Neglecting this responsibility is to guarantee the further indoctrination of home-grown radicals and more death and destruction.
Lastly, to address the challenges of the future, we must also look to our past. One of the most important legacies of the Second World War - perhaps the most positive legacy - is the creation of a new system of international justice, grounded in the Geneva Conventions, created at the Nuremberg Trials and updated through the International Criminal Court.
Thanks to the Nuremberg Trials, it was above all the Nazi ideology that was outlawed and declared criminal. Now it is time to build on these lessons and establish a special tribunal to condemn terrorism and the radical ideologies that support it.
It is time to bring terror leaders and their foot soldiers to justice for their war crimes, crimes against humanity and genocide. They must not escape accountability for what they are doing.