We've seen many historic moments over the past 12 months, and yesterday was yet another.
In her speech, the Prime Minister confirmed what many of us have known for some while: that this Conservative Government has decided to put immigration policy over and above what is in the national economic interest - without even attempting to address the two together.
Giving up on our membership of the EU Single Market before negotiations have even begun is a gamble on all our futures.
This market of 500 million consumers, who buy 44% of everything we sell as a country, has brought huge benefits for Britain's manufacturing industries and service sector, for workers rights, consumer protections and environmental standards.
Yet the Prime Minister has ruled out even trying to retain our membership, despite the serious implications this has for jobs, living standards, inward investment and growth.
She also repeated the Chancellor's threat that Britain will change our "economic model" if we don't get what we want.
This is no way to get agreement from the remaining EU countries. The Prime Minister should be building bridges, not issuing threats, if she wants to get the best result from the negotiations.
Claiming we could walk away because "no deal is better than a bad deal" could not be further from the truth.
No deal would be the worst possible deal for Britain, because if we end up falling back on WTO rules it could mean increased tariffs on around 90% of the goods we export to the EU, making British businesses less competitive. It could also mean increased costs for UK consumers if EU companies face tariffs in return.
Worst of all, threatening to turn us into some kind of off-shore tax haven in an attempt to stay competitive and lure companies to the UK would be a disaster for the vast majority of people in this country. It would not help create good jobs that pay a decent wage in every region, or provide the funding our public services desperately need, but instead benefit a tiny minority of already wealthy people.
Many of those behind the Vote Leave campaign have long championed this small state, low tax, deregulated, trickle-down vision for Britain, where a few succeed and the majority pay a bitter price. But this is not what the vast majority of people in Britain want or voted for, either in the Referendum or the general election.
Labour must speak up for jobs and growth, and for the real changes we need to ensure our economy works for everyone, not just a few at the top.
Whilst the economy is growing, growth is still based in too few sectors and regions and is too reliant on cheap credit and house prices.
We have serious skills gaps in areas like science and engineering, and we invest too little in infrastructure and research and development.
With half of all British households facing a decade of stagnating wages, many people rightly feel the economy isn't working for them.
I am under no illusions. I know from my own constituency that many people voted to leave the EU in order to control immigration. But the Hard Brexit which the Prime Minister now champions will not solve the problems my constituents or the economy face, and in reality risks making them far worse.
This is not a popular or easy argument to make. But true leadership is about more than holding a mirror up to people's anger and despair. It is about providing real solutions to the problems they face.
Those of us who believe in progressive politics will not be bullied into silence by the hard-line Brexiteers. We will show the courage of our convictions and stand up for Britain's national economic interest. We have the fight of our lives on our hands.
Liz Kendall is the Labour MP for Leicester West