LONDON, Oct. 19 (Xinhua) -- British Prime Minister Boris Johnson urged politicians in the House of Commons Saturday to back the Brexit deal he has reached with the European Union (EU).

Members of Parliament (MPs) gathered in the Houses of Parliament for the first Saturday sitting in almost 40 years to vote on whether to accept the deal that will lead at the end of this month to Britain leaving the EU.

During the 24 hours before the debate started 9:30 a.m. local time (0830 GMT), Johnson and his Conservative Party managers, known as whips, contacted MPs who had expressed opposition or concerns to the deal.

Hours of debates faced MPs in the famous wood-paneled chamber ahead of the voting, not due to even start before 3:00 p.m. local time (1400 GMT).

Although Downing Street has expressed cautious optimism that they would reach the 320 votes needed to pass the deal, opponents of the deal are likely to push for a number of amendments that could threaten to delay or defeat Johnson's deal when the voting starts.

Each round of voting takes about 30 minutes, which could mean the critical final vote won't come until early Saturday evening.

Britain's Saturday national newspapers reported a list of MPs who had been won over to Johnson's deal after expressing earlier opposition.

The consensus opinion among political commentators was that the eventual vote is too close to call, with a dead-heat suggested by some observers.

Johnson, addressing a packed Commons, told MPs: "Now is the time for this great House of Commons to come together and bring the country together today."

Johnson said during the three and a half years since people in Britain voted to leave the EU, the whole experience had been so difficult for the country and so divisive, with families across the country divided.

"Now it is urgent for us to move on, on the basis of the new deal to heal the rift in politics," he said.

He told MPs that politicians in the EU had spoken of Britain being half-hearted in its membership of the bloc.

He said further delay to Britain's departure would be pointless.

"There is very little appetite among EU leaders for any further delay, even of one single day," he added.

If MPs reject the deal later Saturday, Johnson will have to write a letter to Brussels by Saturday night seeking an extension of Britain's membership until the end of January 2020.

Although the House of Commons has passed a government act requiring Johnson to write the letter, the prime minister gave no clue in his speech about whether he intended to do so if he lost the vote.

The leader of the main opposition, Labour's Jeremy Corbyn, attacked the deal Johnson reached in Brussels earlier this week and called on MPs to reject it.

He said Johnson's deal was worse than the deal already rejected three times by the Commons.