Labour is to announce a dramatic policy shift by backing continued membership of the EU single market beyond March 2019, when Britain leaves the EU, establishing a clear dividing line with the Tories on Brexit for the first time.
In a move that positions it decisively as the party of “soft Brexit”, Labour will support full participation in the single market and customs union during a lengthy “transitional period” that it believes could last between two and four years after the day of departure, it is to announce on Sunday.
This will mean that under a Labour government the UK would continue to abide by the EU’s free movement rules, accept the jurisdiction of the European court of justice on trade and economic issues, and pay into the EU budget for a period of years after Brexit, in the hope of lessening the shock of leaving to the UK economy. In a further move that will delight many pro-EU
Labour backers, Jeremy Corbyn’s party will also leave open the option of the UK remaining a member of the customs union and single market for good, beyond the end of the transitional period.
https://www.theguardian.com/global/2017/au…iod-post-brexit
So basically what Corbyn is going for is staying in the EU in all but name. It's a shrewd move on his part and really highlights May's disadvantage in losing her majority because the Remainers and soft Brexiteers will have to support him regardless of his other polices if they feel strongly enough about the issue. The worry is that there are lot of Remainers and soft Brexiteers in the Tory ranks.