Brexit opponents rally to delay or stop Boris Johnson deal before October 31

First hurdle is to secure a majority on Saturday but even then leaving on Halloween is not guaranteed

Boris Johnson, UK Prime Minister, left, and Jean-Claude Juncker, the EU Commission President, say a Brexit deal has been reached. Images: AFP / Reuters

Britain has agreed a Brexit deal with Brussels that simultaneously allows for London to strike global free trade deals while compromises over the Northern Ireland's borderless trading relationship with Dublin.

If the deal is ratified it is due to come into force by the end of this month. On October 31 the UK plans to withdraw from the EU after 46 years of membership of the now 28-strong bloc.

There are significant hurdles still to overcome to get to that moment. The first comes on Saturday when for the first time since the Falklands War in 1982 the House of Commons will sit at the weekend to give approval to the revised Withdrawal Agreement.

Boris Johnson is currently more than 40 votes short of a majority in the House. To win a vote on Saturday, Mr Johnson must secure support from 21 ex-Conservatives as well as a large chunk of opposition MPs and independents.

The combined opposition could instead seize control of the business for the day and force the government to instead extend the departure date beyond October. If he is rebuffed look for Mr Johnson to try to trigger a general election in which he asks the country to back him and the deal agreed on Thursday.

If he wins the day on Saturday, the prime minister has told Brussels that it is possible to ratify the agreement within six sittings, or before the end of the month. Jeremy Corbyn, the embattled Labour leader, threatened to scupper this timetable next week by proposing a vote on putting the agreement to a referendum.  That could mean an even longer delay to Brexit of at least six months.

After a long period of sitting on the fence, Mr Corbyn has now confirmed he will prioritise a second referendum to affirm or reverse the 2016 result. "This sell out deal won’t bring the country together and should be rejected. The best way to get Brexit sorted is to give the people the final say in a public vote," he said.

A vibrant remain movement plans a large rally for a second referendum outside parliament on Saturday and many Britons still hope the UK will ultimately revoke the decision to leave.

Assuming Britain does leave the EU on October 31, the deal with Brussels means that nothing will change in the relationship during a transition period, scheduled to run until the end of 2020.

The special provisions for Northern Ireland will then run for four years. The provision would be extended by four years with the approval of a majority of the members of  the Belfast assembly and eight years if the unionist and nationalist communities give their approval.

For Mr Johnson the key points are the previous backstop kept Northern Ireland in the EU customs territory and did not have an expiry date. Northern Ireland will now be in the new independent UK customs zone but have a complex set of arrangements granting it access to the EU's single market. By including an opt out after four years, the arrangement loses the "undemocratic" aspect of the backstop.

Meanwhile the UK as a whole will be able to commence negotiations on Free Trade Agreements with the EU, US, Australia and elsewhere from November 1. If ready in these could come into force from January 1, 2021.

Thursday's agreement envisages a future partnership between the EU and Britain that ensures "no tarrifs, fees, charges or quantitative restrictions" on trade.