The Green Party will pile pressure on Labour to pursue closer ties with the European Union after members backed a motion calling for the party to fight to rejoin.
Party members used the second day of the Greens’ conference in Manchester to vote for a change that will see it fight for “much closer relations with the EU”.
The change means that the party’s official position is now that Britain should seek full membership of the bloc “as soon as the political will is present”.
In the meantime, it means the party will “press the government to be braver and bolder in overcoming the negative impacts of Brexit”.
Ellie Chowns, one of the four Green MPs, said: “There are win-win first steps that the new government should be taking today. For instance, working with the EU to tackle the twin crises of climate breakdown and biodiversity loss would deliver the change we need and create public confidence.
“We should also rejoin the customs union to begin to overcome the obstacles that small businesses have faced in trading with our closest partners since Brexit.”
The policy was in the Green Party’s general election manifesto, which saw it gain four MPs and win almost two million votes.
Ms Chowns, MP for North Herefordshire, said: “While joining the Single Market would provide benefits in terms of free movement of people, goods, services and capital, membership of the Single Market without membership of the EU would not be an ideal long-term solution because the UK would not be a full partner in decision-making processes.”
The party backs the use of so-called citizens’ assemblies, where representative groups of ordinary people are brought together to deliberate on issues, to discuss membership of the EU.
Any move to rejoin the customs union or the EU itself would face furious opposition from Brexiteers. It would also threaten to reopen the divisions seen during years of wrangling over Britain’s departure from the EU.
The vote adds to the issues the Green Party has vowed to use to pile pressure on Labour, after speeches from co-leader Adrian Ramsay saw the party attack Sir Keir Starmer’s refusal to lift the two-child benefit cap and Labour’s decision to withdraw the winter fuel payment from millions of pensioners.
Deputy leader Zack Polanski addressed the conference, slamming Labour’s refusal to implement a full suspension of arms sales to Israel.
Sir Keir is pursuing a reset of relations with the EU after years of negotiations by Conservative prime ministers around Brexit left ties strained.
But, with the PM on a visit in Ireland to meet Taoiseach Simon Harris, deputy Irish MP Michael Martin warned Sir Keir there will not be an “a la carte” menu of Brexit reforms for him to pick and choose from.