Prime Minister's Office, 10 Downing Street
Read more about the UK government response to the Malaysia Airlines flight MH17 disaster.
Like the horror of Lockerbie in 1988 when I was a young man, the images of the burnt-out Malaysian plane, 298 victims and their personal effects strewn across the wheatfields and villages around Grabovo in eastern Ukraine will never leave me.
10 of our own citizens died; we grieve for them this weekend. So too did 27 Australians, including members of a family who had previously lost relatives on flight MH370; 43 Malaysians and 192 Dutch citizens also died a huge blow to our friends and allies. We stand shoulder to shoulder with those countries and with all those affected by this outrage.
But alongside our sympathy there is also anger. Anger that this could happen; anger that a conflict that could have been stopped by Moscow has been fomented by Moscow; anger that some in the West, instead of finding the resolve to deal with this issue, have simply hoped it would go away.
We must establish the full facts of what happened. But the growing weight of evidence points to a clear conclusion: that flight MH17 was blown out of the sky by a surface-to-air missile fired from a rebel-held area.
If this is the case then we must be clear what it means: this is a direct result of Russia destabilising a sovereign state, violating its territorial integrity, backing thuggish militias and training and arming them.
We must turn this moment of outrage into a moment of action. Action to find those who committed this crime and bring them to justice. But this goes much wider than justice.
In Europe we should not need to be reminded of the consequences of turning a blind eye when big countries bully smaller countries. We should not need reminding of the consequences of letting the doctrine of might is right prevail. We should not need to be reminded of the lessons of European history.
But we do. For too long there has been a reluctance on the part of too many European countries to face up to the implications of what is happening in eastern Ukraine.
Sitting around the European Council table on Wednesday evening I saw that reluctance at work again.
Some countries, with Britain at the forefront, have consistently pushed for action that reflects the magnitude of the long-term threat. They tend to be the countries with the closest physical proximity to Russia and the most direct experience of what is at stake. Their own independence and nationhood have come at a high price. They never forget it. But others seem more anxious to make this a problem to be managed and contained, not a challenge to be met and mastered.
Elegant forms of words and fine communiqus are no substitute for real action. The weapons and fighters being funnelled across the border between Russia and eastern Ukraine; the support to the militias; the half-truths, the bluster, the delays. They have to stop.
Some international crises are insoluble. Not this one. If President Vladimir Putin stops the support to the fighters in eastern Ukraine and allows the Ukrainian authorities to restore order, this crisis can be brought to an end. Of course there must be proper protections for Russian-speaking minorities. These issues can be addressed. But the overriding need is for Russia to cease its support for violent separatists.
If President Putin does not change his approach to Ukraine, then Europe and the West must fundamentally change our approach to Russia.
This is not about military action, plainly. But it is time to make our power, influence and resources count.
Our economies are strong and growing in strength. And yet we sometimes behave as if we need Russia more than Russia needs us and the access we provide to European markets, European capital, our knowledge and technological expertise.
We dont seek a relationship of confrontation with Russia. But we must not shrink from standing up for the principles that govern conduct between independent nations in Europe and which ultimately keep the peace on our continent.
So let us be clear about what needs to happen.
First, there must be immediate access to the crash site and the crime scene must be preserved. The remains of the victims must be identified, treated with proper respect and dignity and returned to their families. There must be a ceasefire. And there must be a full investigation into what happened. Russia will have plenty of information about these events which it must make fully available and straight away.
Second, Russia must immediately halt supplies and training for the rebels. They do not represent the people of Ukraine. Without Russian support they will wither.
Finally, we must establish proper long-term relationships between Ukraine and the European Union; between Ukraine and Russia; and, above all, between Russia and the European Union, NATO and the wider West.
What form that relationship takes rests on how Russia responds to this appalling tragedy. Russia can use this moment to find a path out of this festering, dangerous crisis. I hope it will do so. But if that does not happen then we must respond robustly.
Nearly 25 years ago Britain hosted the NATO summit that ended the Cold War and began the process of ushering Russia back into the councils of the world.
In 6 weeks time Britain will host a NATO summit in Wales at which the relationship with Russia will again take centre stage. It is up to Russia which path that relationship now takes.
For the latest updates on the NATO Summit, visit the NATO Summit Wales 2014 homepage and @NATOWales on Twitter.