Theresa May tried and failed three times. Now it is Boris Johnson's turn to try to break a Brexit agreement through the British Parliament. But having an agreement in place is an important first step, explains James Savage.

- This is a first step in this process, which means that there is something new for Parliament to take a position on.

- But the question marks are, as always with Brexit, a huge number, says James Savage.

Support from several directions is required

A major obstacle for the incumbent government is that the Northern Ireland support party DUP has announced that they will not vote for the agreement.

And even if the DUP were to change, support from additional groups is likely to be needed to reach a majority in Parliament. For example, the more pro-European Tory MPs who were excluded from the party earlier this year.

- You need to get them into the party again but it will be difficult. This agreement means an even tougher Brexit than Theresa May's agreement, says James Savage.

If you get both the DUP and the excluded Tory members, you probably have a majority in Parliament. But it also assumes that the more Euro-skeptical parliamentarians within the Tory party are voting for the agreement.

- Boris Johnson has to bring everyone along, says James Savage.

Hope on Labor support

Another option is that Boris Johnson may be supported by a group of Labor MPs.

- There are about 30 Labor members who say they want an agreement and would be prepared to vote through an agreement, but maybe not any agreement, says James Savage.

- However, they will be put under pressure by the Labor leadership who instead want the agreement to be approved by a new referendum.

Boris Johnson is on his way to the EU summit, how will he manage to do all this before Saturday when Parliament may vote?

- He will hold talks with all groups, but it will not be easy. It will be very, very difficult, says James Savage.