All of us have been sickened beyond words by the appalling attack in Paris.
And then by the dreadful events in Copenhagen, with the murder of a young Jewish volunteer guarding the synagogue.
When I was at school, I remember watching "The World at War", listening to the voice of Laurence Olivier and learning about the Holocaust.
I thought it was part of history and could never happen again.
But somehow, after all the horrors of the past, people are once again being targeted simply for being Jewish.
During my visits to Yad Vashem and Auschwitz last year I had some time to reflect on where bigotry and prejudice can lead.
It doesn't matter how many books you've read, documentaries you've studied, films you've seen…
…it's only when you stand under that sign, "arbeit macht frei"...
…when you walk alongside those train tracks that brought millions to their death…
…when you see the children's clothes, the parents' luggage, the hair…the gas chambers and the ovens...
…that the horrific enormity of it all comes home to you.
I found that I kept asking myself some difficult questions: 'what would I have done if I had seen this terrible crime unfolding in front of me?'
Would I have hidden my Jewish neighbours?
Would I have had the courage to speak out against the murder?
Would I have joined the resistance?
Would I have tried to do any of these things if I placed my family at risk?
These are really difficult questions.
I suppose that you never know precisely how you would behave until you are faced with the choice.
But as Prime Minister of this country there is one thing that that I do know.
At a time when once again the Jewish communities of Europe feel vulnerable...
...and when anti-Semitism is at record levels here in Britain...
...I will not stand by.
I will not turn a blind eye to the threats that the community faces.
If the Jewish community does not feel secure then our whole national fabric is diminished.
It is not just about the enormous contribution you all make to our society - it is more profound than that.
It is a measure of the vigour of our institutions and the health of our democracy that the Jewish community feels safe to live and flourish here.
It is about the strength of the values that we stand for.
The kind of country we are.
So let me tell you this.
We are going to fight anti-Semitism with everything we have got.
There will be no excuses. No exceptions. No justifications.
Over generations we have built something incredible in our country: a multi-ethnic, multi-faith democracy - and we are not going to let anyone destroy it.
Let me be clear.
No disagreements on politics or policy can ever be allowed to justify racism, prejudice or extremism in any form in our society.
We will not have it.
So first, it's about keeping people safe.
Second, it's about tackling the causes of this extremism.
And third, it's about speaking up loudly and proudly for British values.
Let me take each in turn.
No modern democracy is ever totally safe, of course not.
But we are doing everything we can.
We have already protected police budgets for counter-terrorism...
...and provided an additional £130 million for our security services over the next two years following the increase to the UK threat level in August.
We know that if we want to stop terrorists we need to know what they are planning and restrict their movements.
So we have introduced two new pieces of legislation in the last year.
One to access terrorist communications...
...and another - the Counter-Terrorism and Security Act - to seize passports, stop suspects travelling, and relocate terror suspects in the UK away from their extremist networks.
And we're continuously looking at how we can strengthen our capabilities, learn lessons, and stay one step ahead of the terrorists.
At a time when see young people being drawn overseas who perhaps aren't already known to our intelligence agencies...
...we need to do more to ensure we have the capacity at our borders to identify those who could be at risk.
So today I am announcing an extra £13 million for our border force and police...
...including funding so that we have the latest technology to analyse passenger data and get to those young people before it's too late.
This will help protect us all.
But the Jewish community is being specifically targeted.
So CST doesn't just need money to carry on doing what it does so well.
It needs more money to do a lot more of it.
We all need to dig deep tonight and give as much as we can.
And I include the government in that.
We already provide £2 million a year for security for Jewish state schools - something that has been championed brilliantly by Matthew Offord.
But as Mike Freer put it to me what if an attack happened at a private school?
How would we feel if we knew we could have done more?
That's not a thought I am prepared to entertain.
So today in the Budget, we have committed over £7 million of new money to fund guards for all Jewish private schools and colleges.
So at every school - state or private, north or south - the government will play its part in protecting your children.
But that's not enough on its own.
CST, the Jewish Chronicle and the All-Party Parliamentary Group against anti-Semitism have all highlighted the risk to synagogues and other potentially vulnerable Jewish community buildings.
So we're going to help with this too.
Tonight I can announce a further £3 million.
That's over £10 million of new money for security - this year - and every year - for as long as necessary.
And we're doing something else too.
I want CST to have a state of the art Mission Control centre...
...with closed-circuit television command and control and the ability to respond rapidly to those who need their help right across our Jewish communities.
And today I can announce an additional £1.5 million in capital to help you build it.
But we will not win this battle with security measures alone.
We need to tackle the causes of the terrorist threat not just its consequences.
And that means taking on and defeating Islamist extremism…
…a poisonous ideology that perverts the Islamic faith in an attempt to justify the most sickening barbarism and brutality.
We know what this so-called world view includes.
The idea that Muslims are persecuted all over the world as a deliberate act of Western policy.
The peddling of lies: that 9/11 was a Jewish plot or that the 7/7 London attacks were staged.
Or that there are times and places when suicide bombs and terrorism are somehow ok.
They claim that saying these things is exercising free speech.
I say: no it isn't. It's incitement. And we are not going to stand for it.
So we are tackling this so called non-violent extremism wherever it is found.
On the internet - by taking down more than 75,000 pieces of extremist material since 2010.
In our schools, universities and prisons - with a public duty in the new Counter-Terrorism and Security Act to prevent people being drawn into terrorism.
And in our wider communities - by stopping the funding of organisations that promote extremism...
...and giving the Charity Commission new money and new powers to investigate charities with extremist links.
And yes, we're keeping those hate preachers out.
The Home Secretary has banned more hate preachers than any of her predecessors.
Britain said no to Zakir Naik, Yusuf al-Qaradawi and Judon Mumbala Umbala.
And we kicked out Babar Ahmad, Abu Hamza and Abu Qatada too.
We are a tolerant country - but if you preach terror you are not welcome here.
And if I am returned as Prime Minister at the election, I will also introduce new banning orders for extremist groups that are not covered by the existing laws relating to terrorism…
…with new civil powers to target extremists who stay just within the law but still spread poisonous hatred.
We would not sit back and allow right-wing extremists or Nazis to recruit support in these ways.
So we will not allow Islamist extremists this opportunity either.
Third, we need to shout more loudly and more proudly about our British values.
Over generations we have built something incredibly special in this country.
We are a great multi-racial, multi-ethnic society.
And we should celebrate that.
Our young people should understand the freedoms we have fought to defend.
The right to free speech. The right to demonstrate peacefully.
Democracy. Property rights. The rule of law and equality before the law.
A free media.
And there is no community in our country more proud of these freedoms and more proudly part of Britain than our Jewish community.
You have produced Prime Ministers, industrialists, writers, actors, scientists, inventors and Nobel Prize winners.
All proud to be Jewish and proud to be British too.
And there is no better example of this than some of the Holocaust survivors I have met over the last year.
People who have been through the most harrowing moments of humanity and who have come to this country and made great lives for themselves here.
People who have lived ten, twenty lives for every one that didn't make it...
...who have gone on to become everything from great musicians and teachers to Olympic weightlifters.
Every one of them proud to call Britain their home.
And I am delighted that in taking forwards the work of the Holocaust Commission...
...the new UK Holocaust Memorial Foundation is conducting the biggest audit of survivor testimony in British history.
It is right that the stories of these incredible survivors, incredible Jews, incredible Britons should be recorded and preserved.
And thanks to the brilliant work of Mick Davis and the Holocaust Commission...
...this survivor testimony will form the foundation of the new Learning Centre and national Holocaust Memorial.
The government is giving £50 million to kick start a society-wide fundraising effort for this...
...so that the lessons of the Holocaust can be learnt by young people in every part of this country for generations to come.
YOU WILL NEVER BE ALONE
Lloyd, in your introductory remarks you didn't just ask whether the Jewish people in our country will be safe.
You also asked if they would be alone.
For as long as I am Prime Minister, you will never be alone.
When people talk of trying to boycott Israel - you will never be alone.
When students on campus are afraid…
…when Shechita is under threat…
…when Jewish institutions need extra security - you will never be alone.
And when Israel is under attack from rockets or terror tunnels - you will never be alone.
As I said in the Knesset, I will always stand up for the right of Israel to defend its citizens, a right enshrined in international law, in natural justice and fundamental morality.
Israel is an extraordinary nation - and even more extraordinary when you think where it is.
On its doorstep...
...the barbarism of ISIL...
...the tyranny of Assad...
...Hamas and Hezbollah a missile's distance away...
...Iran looming nearby with nuclear ambitions...
...and terrorists all around, hell-bent on doing it harm.
And yet Israel stands as a democracy...
...a place where people can have their say, just as they did yesterday.
And I congratulate Prime Minister Netanyahu and look forward to working with the new Israeli government.
With me you will always have a British Prime Minister whose belief in Israel is unbreakable and whose commitment to Israel's security will always be rock solid.
And to you, the Jewish community in Britain, I say this:
For as long as I am Prime Minister, I will stand with you, work with you, celebrate what you do and ensure we do everything possible to keep you safe.
And I truly believe that we will succeed.
The battle against Islamist extremism is the battle of our generation. It won't be defeated overnight.
It will take patience and resolve. And there may well be setbacks along the way.
But as in the past, I believe in the end that our values will win through.
Back in January I joined the march on the streets of Paris surrounded by placards saying: 'je suis Juif'.
In the aftermath of one of the darkest moments in Europe in recent times, people of all ages and all backgrounds came together to show solidarity with those who had suffered.
In the face of those who tried to suppress our values, the voice of free speech responded ever louder.
As so often in the worst of times, the best of humanity came shining through.
Together, we will beat anti-Semitism.
And we will make sure Britain remains a country that Jewish people are proud to call home - today, tomorrow and for every generation to come.