Theresa May's Brexit deal has been defeated in the House of Commons.
After months of debate and build-up, the withdrawal agreement was overwhelmingly rejected by MPs in the crucial 'meaningful vote'.
The final vote was 432 to 202, amid opposition to the agreement from opposition parties, the DUP and more than 100 Conservative MPs.
It's the heaviest defeat for a British government since the 1920s.
MPs have previously voted to demand the government comes forward with an alternative proposal or 'Plan B' by Monday.
Labour's Jeremy Corbyn confirmed his party had tabled a motion of no confidence in the British government, in the wake of what he described as a "catastrophic" defeat.
Speaking after the defeat, Mrs May confirmed her government will make time for the no confidence motion to be debated tomorrow.
The Irish Government has tonight released a statement saying it "regrets the outcome" of tonight's vote, and will consider the next steps with EU partners.
The statement adds: "Regrettably, the outcome of tonight’s vote increases the risk of a disorderly Brexit. Consequently, the Government will continue to intensify preparations for such an outcome.
"The Irish Government recognises, however, that a disorderly Brexit is a bad outcome for everyone, not least in Northern Ireland. It is not too late to avoid this outcome and we call on the UK to set out how it proposes to resolve this impasse as a matter of urgency."
European Council President Donald Tusk was one of the first European officials to respond to the vote - appearing to suggest staying in the EU was the only positive solution for the UK.
If a deal is impossible, and no one wants no deal, then who will finally have the courage to say what the only positive solution is?
— Donald Tusk (@eucopresident) January 15, 2019
In a statement, European Commission President Jean-Claude Juncker urged the UK "to clarify its intentions as soon as possible".
Jean-Claude Juncker. Picture by: Vadim Ghirda/AP/Press Association Images
He said: "The European Commission, and notably our Chief Negotiator Michel Barnier, has invested enormous time and effort to negotiate the Withdrawal Agreement. We have shown creativity and flexibility throughout.
"I, together with President Tusk, have demonstrated goodwill again by offering additional clarifications and reassurances in an exchange of letters with Prime Minister May earlier this week."
He added: "The risk of a disorderly withdrawal of the United Kingdom has increased with this evening's vote. While we do not want this to happen, the European Commission will continue its contingency work to help ensure the EU is fully prepared."
DUP leader Arlene Foster, who opposed the deal, said an 'unmistakable message' had been sent that the deal is rejected.
She argued: "Mrs May will now be able to demonstrate to the Brussels’ negotiators that changes are required if any deal is to command the support of Parliament.
"Reassurances whether in the form of letters or warm words, will not be enough. The Prime Minister must now go back to the European Union and seek fundamental change to the Withdrawal Agreement."
Picture by: Tim Ireland/Xinhua News Agency/PA Images
MPs were due to vote on a series of amendments - two opposition motions and two from pro-Brexit Conservatives.
However, it emerged shortly before the voting was due to start that all but one of the amendments were being dropped.
The ones that were dropped include Jeremy Corbyn's motion which called for the rejection of Mrs May's deal, a "no-deal" Brexit to be ruled out and for MPs to instead back Labour's plans for a permanent customs union.
The Tory Brexiteer motions, meanwhile, included one calling for the UK to be given the explicit power to terminate the backstop without permission from the EU.
That vote went ahead, but was easily defeated - with 24 'yes' votes to 600 for 'no'.
Jeremy Corbyn this evening repeated his call for a general election, saying a new government with a clear mandate is needed to break the Brexit deadlock in the House of Commons.
The EU has repeatedly ruled out the prospect of any fundamental changes to the withdrawal deal, and will likely reject any efforts to water down the Irish backstop plans.
However, senior EU officials - including Tánaiste Simon Coveney - have indicated they'd be open to considering a request for an extension of Article 50.
An EU commissioner earlier told reporters that Mr Juncker has cleared his diary for tomorrow in case Mrs May seeks emergency talks on Brexit.
— Henry McKean (@HenryMcKean) January 15, 2019
Following another week of debate in the Commons, the British Prime Minister was the final person to speak before the voting began this evening - with Mrs May saying it was the most significant vote any MPs would ever be part of in their political careers.
She told MPs: "This is an historic decision which will set the future of this country for generations."
She argued that a second referendum would lead to "further division", while a no deal exit would not be the best outcome for the UK.
Mrs May also suggested that a general election would only leave any new government with the same options on the table.
Speaking about the prospect of negotiating another deal with the EU, she insisted: "No such alternative deal exists."
She also addressed the contentious issue of the Northern Ireland backstop, telling MPs: "The key thing to remember is this isn't a commitment we're making to the European Union - it's a commitment we're making to the people of Northern Ireland and Ireland.
"No-one wants to see the return of a hard border... but it is not enough to simply make those assertions. We have to put in place arrangements that deliver those ends.
"No backstop simply means no deal."