Updated with initial reactions -

British MPs overwhelmingly rejected Prime Minister Theresa May's Brexit deal for a second time on Tuesday, pitching Britain into the unknown just 17 days before it is due to split from the European Union.

The House of Commons voted by 391 to 242 to reject the divorce deal, even after May secured further guarantees from Brussels over its most controversial elements.

After the vote Mrs May said she was profoundly disappointed but she remained committed to delivering Brexit in an orderly manner. 

EU Council President Donald Tusk regretted the outcome.

"On the EU side we've done all that's possible to reach an agreement. It's difficult to see what more we can do. If there's a solution to the current impasse it can only be found in London. Today's vote has significantly increased the likelihood of no-deal Brexit," he said.

On Wednesday MPs will vote on whether or not to take no-deal off the table. If it is taken off the table, they will vote on Thursday on seeking an extension of the Brexit March 29 deadline. 

A spokeswoman for European Commission President Jean-Claude Juncker said that should there be a UK reasoned request for an extension, the EU27 would stand ready to consider it and decide by unanimity.

Tuesday's vote risks unleashing economic chaos, as Britain is scheduled to end ties with its biggest trade partner after 46 years on March 29, no matter what.

Appealing to MPs in a voice half-breaking due to a cold, May had urged them to avoid the "economic shock" of leaving without an agreement.

But she also warned eurosceptics, many of whom have campaigned to leave the EU for their whole careers, that if her deal failed, so might Brexit.

May has promised to allow MPs to vote on a "no deal" option on Wednesday and if that is rejected, to decide on Thursday whether to ask the EU to delay Brexit.

"If this vote is not passed tonight, if this deal is not passed, then Brexit could be lost," she said before the vote.

However, eurosceptics believe the deal is so bad it is worth the risk of leaving with no plan.

"We must take what now seems to be the more difficult route but in the end the one that preserves our self-respect," said former foreign minister Boris Johnson, a favourite to succeed May if she steps down.

"It is to leave on March 29 as required by law and to become once again an independent country able to make our own choices."

- Not a single change -
After MPs first rejected the 585-page Brexit deal in January, May promised changes to the hated backstop plan which is intended to keep open the border with Ireland.

Weeks of talks failed to make a breakthrough, but May made a last-minute trip to Strasbourg to meet EU leaders on the eve of the vote.

She announced she had secured the promised "legally binding changes" to the backstop, which would keep Britain in the EU's customs union if and until a new way was found to avoid frontier checks.

But hours later, however, Attorney General Geoffrey Cox said the additions would not completely allay MPs fears of being trapped in the arrangement forever.

It did not take long for Brexit-supporting MPs in May's Conservative party, and her allies, Northern Ireland's Democratic Unionist Party (DUP), to declare their opposition.

Opposition Labour leader Jeremy Corbyn also urged parliament to vote down May's plan. 

"After three months of running down the clock, the prime minister has, despite very extensive delays, achieved not a single change to the withdrawal agreement," he said.

After the vote, he said Mrs May's deal was 'dead'.

Some eurosceptics changed their mind, however, urging their colleagues not to risk everything.

Former minister Edward Leigh said: "You may not like the deal, it's not perfect, but it delivers Brexit and let's go for it."

The pound, which has been highly volatile since the 2016 referendum which saw Britons narrowly vote to leave the EU, made gains against the euro after May's deal on Monday but fell sharply on Tuesday as it became increasingly clear the deal would be defeated.

- 'No third chance' -
The backstop is designed to protect the peace process in Northern Ireland, which involved the removal of border checks with EU member Ireland.

Brexit supporters wanted a unilateral way out of it, or a time limit to the arrangement, but the EU said this would make it worthless.

But leaders across Europe also united behind a message that this was the best and final offer Britain could expect.

"There will be no third chance," European Commission chief Jean-Claude Juncker said after his talks on Monday with May.

If MPs vote against a "no deal" exit on Wednesday, and want to postpone Brexit, the other 27 EU nations would need to agree.

Their leaders will meet in Brussels for a summit on March 21-22.

But any postponement may have to be short-lived. Juncker on Monday said Brexit "should be complete before the European elections" at the end of May.

PN: Outcome is not good for Malta

In a reaction to the Commons vote, the Nationalist Party said this was not good
news for Malta and it was not good news for Europe or the UK.

"A no-deal Brexit could have lasting effects even on Malta and this is why the Nationalist Party has insisted time and time again in Parliament and outside, that the Maltese Government should be fully prepared for such an eventuality," the party said.

It also insisted that the Maltese government should keep the Maltese resident in the UK well informed about their rights and obligations in a no-deal scenario.