The Democratic Unionist Party has denied “cash for votes” suggestions after the chancellor was sent into talks designed to win its support for the Brexit deal.

“We are not discussing cash in these discussions,” Nigel Dodds, the DUP’s Westminster leader, insisted – amid government pressure on the party to switch sides in next week’s repeat “meaningful vote”.

Instead, Mr Dodds said Theresa May must do more to convince the party that the deal would not breach its “red line” that Northern Ireland must not be treated differently from the rest of the UK.

Philip Hammond’s surprise appearance at the talks raised eyebrows because the £1.5bn arrangement for the DUP to prop up the Tories in power expires in June and would have to be renewed.

But Mr Dodds said: "The chancellor of the exchequer is obviously a key member of the government, but he is also responsible for HMRC and the whole issue of their involvement in customs and other regulatory issues is a key concern for us.”

“From day one, our focus has been on the red line of how Northern Ireland is treated separately from the rest of the UK. That is the issue that has been the priority concern for us,” he continued

Three other cabinet ministers attended the talks – underlining the government’s belief that a DUP switch is the likely route to overturning this week’s crushing defeat.

Britain Before Brexit: Northern Ireland Show all 12 1 /12 Britain Before Brexit: Northern Ireland Britain Before Brexit: Northern Ireland Derry, Londonderry A garage door displaying unionism, bolted shut, like a visual representation of Brexit Britain, locked to outsiders, safeguarding what’s inside Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry Rossville Street, the site of Bloody Sunday, where messages demand a severance with England. From this perspective, Britain is England in sheep’s clothing, the real empire, the centre of colonial power Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Bangor A political message in paint not yet dry, still forming, setting, adjusting, or in old paint finally eroding, melting away Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Bangor Moral judgement frames a residential view. The message seeks to make everybody involved in the religious narrative: those who don’t believe are those most in debt Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Castlerock The beach is sparse and almost empty, but covered in footprints. The shower is designed to wash off sand, and a mysterious border cuts a divide through the same sand Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Belfast Two attempts to affect and care for the body. One stimulated by vanity and social norms and narratives of beauty, the other by a need to keep warm in the winter night Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Belfast The gate to an unclaimed piece of land, where nothing is being built, where no project is in the making, where a sign demands the creation of something new Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry Under a motorway bridge a woman’s face stares, auburn and red-lipped, her skin tattooed with support for the IRA and a message of hostility to advocates of the Social Investment Fund Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry The Fountain Murals, where the curbs and the lampposts are painted the red, white, and blue of the Union Flag. A boy walks past in the same colours, fitting the scene, camouflaged Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Coleraine A public slandering by the football fields, for all to see or ignore. I wonder if it’s for the police or for the community Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Belfast A tattoo parlour, where the artist has downed tools, momentarily, bringing poise to the scene, which looks like a place of mourning, not a site of creation Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry A barrier of grey protects the contents of this shop, guarding it from the streets outside, but it cannot conceal it completely, and the colours of lust and desire and temptation cut through Richard Morgan/The Independent

Dozens of anti-deal Tories, plus some Labour MPs, are expected to swing behind the agreement if the Northern Ireland party abandons its opposition over the Irish border backstop.

The talks came as the government paved the way for another crucial vote to change the Brexit departure day – if and when an Article 50 extension is agreed at next week’s EU summit.

A written statement confirmed no act of parliament is required, just a positive vote in both the Commons and Lords, so domestic law matches the agreement reached in Brussels.

Meanwhile, Jeremy Corbyn was asked to join cross-party talks by the leaders of the SNP, Liberal Democrats, Plaid Cymru and the Green Party, to push for a second referendum.

Ian Blackford, the SNP Westminster leader, said: “I hope Jeremy Corbyn will now join us – after two years of declining invitations to talk.”

Emerging in Whitehall, Mr Dodds also denied discussing the latest legal advice on escape routes from the backstop, after lawyers for the European Research Group of hardline Tories rejected them.

Instead, the focus is on strengthening the so-called “Stormont Lock”, under which Belfast could block any new regulatory barriers in the Irish Sea.

Mr Dodd said the backstop raised the danger “of leaving Northern Ireland behind in single market regulations and the customs union if the rest of the UK went its own way in the future”.