The leader of the SDLP has said a Border poll on a united Ireland should be called after the Brexit negotiations are concluded.

Launching his party’s Westminster election manifesto in Belfast on Tuesday, Colum Eastwood said a referendum on Irish unity would “need to happen after Brexit”.

He did not give a specific date for a plebiscite, but suggested it should take place when the negotiations on taking the United Kingdom out of the European Union are completed.

Mr Eastwood said the SDLP would campaign on creating an “Ireland based on reconciliation and working together”.

He referred to how the British government accepted that, in the event of a vote for unity, that Northern Ireland would rejoin the EU. Mr Eastwood said that, under pressure from Foyle MP Mark Durkan, the British Brexit secretary David Davis accepted that Northern Ireland was “the only place in these islands with an automatic path back into the EU as a result of the principle of consent and the Good Friday Agreement”.

“While others were waving banners, the SDLP made the prospect of a successful unity referendum much more possible because a Border poll is no longer solely the project of Irish nationalism but of pro-European internationalism,” he added. “A unity referendum now has a much broader reach, offering us a return to the European Union as a sovereign country. That’s the kind of progress that’s made by MPs who turn up for work, not just wine receptions and lobbying lunches.”

Mr Eastwood criticised Sinn Féin for refusing to take its seats in the House of Commons, particularly at a time when, he said, there was real prospect of a hung British parliament.

“The only way to take a stand in this election is to take your seats. Shouting from the sidelines will make no difference. With the polls increasingly tightening and the possibility of another hung parliament, every seat and every vote comes into focus at this critical time,” he added at the manifesto launch in the Crescent Arts Centre in south Belfast.

“I have a simple question for the abstentionist MPs – is there nothing more important to you than this one principle? Is there no cause worth fighting for more? Are there no people worth standing up for more? SDLP MPs don’t stand aside for the Tories, we stand up to them. And we’ll be a part of a broad coalition of parties at Westminster coming together to take on Theresa May. ”

Mr Eastwood said the political maths of this election were simple. “A DUP seat will only add to Tory numbers – a Sinn Féin seat won’t even get counted.”

Notwithstanding the expectation of a Tory victory, Mr Eastwood said that with the British Labour fightback in the polls, “there’s every chance that we could see off the Tory government entirely”.

But in the event of a Conservative victory, Mr Eastwood said this election was about “not letting Theresa May have a free hand in the Brexit negotiations”.

On Brexit he accused Sinn Féin of stealing the SDLP’s proposal for special designated status for Northern Ireland within the EU after the Brexit negotiations are sorted. “Those who tried to shout us down have not only joined our campaign for special status, they’ve tried to claim credit for it. Not content with rewriting the past, they’re now trying to rewrite the present. But our focus remains firmly on the future.”

The SDLP primarily is seeking to hold on to its three seats held by three former leaders, Dr Alasdair McDonnell in South Belfast, Mark Durkan in Foyle and Margaret Ritchie in South Down. The SDLP is under most pressure from Sinn Féin in Foyle and South Down, and from the DUP in South Belfast.

Resisting that challenge may require unionists voting tactically for the SDLP in Foyle and South Down. Asked was he seeking unionist support Mr Eastwood said, “We appeal for votes from everybody.”

SDLP Manifesto – Main Points

• Special EU status for Northern Ireland after Brexit.

• Restoring Northern Executive and Assembly.

• Opposing welfare and pension cuts.

• Promoting LGBT rights and same sex marriage.

• Irish language act for Northern Ireland.

• Comprehensive plan to deal with legacy of Troubles.

• Opposing extension of British 1967 abortion act to Northern Ireland.

• Promoting an all-island approach to health and social care.

• More focus on job creation.

Conservatives’ Northern Ireland manifesto

Meanwhile, launching the Conservatives’ Northern Ireland manifesto, Secretary of State James Brokenshire said the conditions for calling a Border poll on unification were “not remotely satisfied”.

“I remain satisfied on the basis of all reliable indicators of the continued support for the devolved administration, the principles and the structures and institutions that are underpinned within the Belfast Agreement (1998) and its successors, and I am very clear that the requirements for a border poll are not remotely satisfied,” he said.

“Obviously, we keep these issues under very close and careful review but I think in terms of the way people vote, that people may vote for one party but that doesn’t necessarily mean they want to see a change to the institutions, that they want to see a change to the foundations that underpin all of that stability that has been achieved from the Belfast Agreement and thereafter.”

Mr Brokenshire said legislation required the incoming government to keep the situation under review. “As I see it, the support for those institutions, the support for Northern Ireland remaining a core part of the United Kingdom, remains very firmly there,” he said.

The Conservative manifesto document rules out any possibility of the region being administered on the basis of joint authority between the UK and the Republic of Ireland if a new powersharing executive is not formed following the resumption of negotiations after the general election.