LONDON (Reuters) - Britain's parliament began a session on Saturday for an unresolved historic vote on Prime Minister Boris Johnson's agreement on Brexit, just 12 days before the UK leaves the European Union.

The House of Commons session, convened on Saturday for the first time since the Falkland War 37 years ago, kicked off at 8:30 UTC to begin discussions that could last throughout the day.

The government, which does not have a majority in the House of Commons, needs 230 votes to approve the deal.

The deal, which was taken at the last minute after tough negotiations, should allow the conditions of separation to be settled after 46 years of common life, allowing a quiet exit with a transition period that will last until at least the end of 2020.

But its success is tied to the approval of parliament, which has adopted a tough stance before. The deputies three times rejected the agreement reached by former Prime Minister Theresa May with the 27 EU member states.

Prime Minister Boris Johnson said Britain would withdraw from the EU at the end of October if parliament rejected an exit deal with Brussels.

He said at the House of Commons session to discuss the Brexit agreement ahead of the vote today that the British economy will regain its strength after Brexit, stressing the need to work to build partnership and strong relations with European friends after Brexit.

The conservative prime minister has made strenuous efforts in recent days to persuade lawmakers to back his deal by holding phone conversations and appearing on television.

He stressed that "there is no better way out" than the agreement he reached to leave the European Union on 31 October, calling on deputies to envision a world of "overcoming" the Brexit obstacle that paralyzed political life three years ago. "I think the nation will feel very comfortable," Johnson said.

If the agreement is approved by parliament, it should be submitted to its European counterpart for ratification.

Johnson insists he would prefer, if he rejects the deal, an exit without agreement on a new deadline after the Brexit was postponed twice. But parliament passed a law requiring it to request a new three-month delay.

Economic circles fear an exit without agreement because, according to the government's own expectations, it could lead to shortages of food, fuel and even medicines.

Opposition parties have announced that they will oppose the agreement. The center-left Liberal Democratic Party (19 votes) and the Scottish Nationalist Party (35 votes) oppose Brexit, the Labor Party (242 votes) sees the new agreement as weakening workers' rights, while environmentalists (the Greens, one vote) consider it not to respect the environment. .

The main opponents of the text are Northern Ireland's Unionists, represented by the Democratic Unionist Party (10 votes) and Johnson's allies in parliament, who say the text gives their county a different status and isolates them from the rest of Britain.

The government hopes to convince some workers and independents, especially deputies who were excluded from the Conservative Party for their opposition to the Brexit without agreement.

An anti - march
Meanwhile, the "People's Vote Campaign" - calling for a second Brexit referendum - hopes hundreds of thousands of people will head to central London on Saturday.

The campaign, backed by pro-EU lawmakers from major political parties, said it wanted to make the march to parliament "one of the biggest and most important protests our country has ever seen." A number of prominent politicians are scheduled to speak at the event, including London Mayor Sadiq Khan and Carolyn Lucas, the only member of parliament for the Green Party.

The march will take place during the special session of parliament today as lawmakers prepare to debate and vote on the Brexit agreement, which Johnson agreed with Brussels.

The People's Voting Campaign said the protesters "will send a loud and clear message to the government and lawmakers that they should trust people, not Johnson, to resolve the exit crisis."

The campaign earlier claimed that about one million people took part in their last march in March, but experts in crowd estimates put the number of participants at between 300,000 and 400,000.

In the 2016 EU exit referendum, 52% of voters chose yes.