Tarnished and in the minority but little scope for compromise as political polarisation has further emboldened unionists

When the Democratic Unionist party this week threatened to paralyse the government’s domestic agenda over Brexit, some Conservatives felt enough was enough and it was time to call the DUP’s bluff.

“Shocking, profoundly undemocratic,” Anna Soubry, a Tory MP from Nottinghamshire, seethed in a radio interview. “It’s breathtakingly irresponsible. They’re a blooming nightmare. Who do they think they are?”

It’s a question reverberating around Westminster and European capitals. Who exactly are these Northern Ireland unionists that prop up – and menace – Theresa May’s government? Why are they forcing the prime minister into a corner and tilting negotiations with the European Union towards possible destruction? And are they bluffing?

Quick guide Brexit and backstops: an explainer Show Hide A backstop is required to ensure there is no hard border in Ireland if a comprehensive free trade deal cannot be signed before the end of 2020. Theresa May has proposed to the EU that the whole of the UK would remain in the customs union after Brexit, but Brussels has said it needs more time to evaluate the proposal. As a result, the EU insists on having its own backstop - the backstop to the backstop - which would mean Northern Ireland would remain in the single market and customs union in the absence of a free trade deal, prompting fierce objections from Conservative hard Brexiters and the DUP, which props up her government. That prompted May to propose a country-wide alternative in which the whole of the UK would remain in parts of the customs union after Brexit. “The EU still requires a ‘backstop to the backstop’ – effectively an insurance policy for the insurance policy. And they want this to be the Northern Ireland-only solution that they had previously proposed,” May told MPs. Raising the stakes, the prime minister said the EU’s insistence amounted to a threat to the constitution of the UK: “We have been clear that we cannot agree to anything that threatens the integrity of our United Kingdom,” she added.

Such questions became more urgent on Thursday as May came under attack from Tory colleagues after conceding that the UK may have to remain tied to EU rules and laws beyond December 2020 in an effort to solve the Irish border conundrum.

If she cannot appease her own party’s Brexiters, the prime minister will need the DUP’s 10 Westminster votes to stand any chance of pushing a deal through parliament. Yet the ostensible allies who shore up her minority government under a confidence and supply agreement now threaten revolt over any Chequers-type deal with regulatory checks between Britain and Northern Ireland.

“There is a lot we cannot support in terms of the government’s domestic, financial, welfare and other legislation,” said Nigel Dodds, the DUP’s Westminster leader. The party would stop short of triggering an election lest Jeremy Corbyn win it, said Dodds.

Some observers in Belfast refer to the DUP’s relationship with the Tories as a “doom loop”. Voters in Carrickfergus, a seaside town in the DUP heartland of East Antrim, see it another way: the party is protecting the union with Britain.

“They’re dependable, they’re safe,” said Trevor Stevenson, 49, a gardener and handyman. “We’re not really worried about other countries.”

John Richardson, 72, said the DUP had his support in Thursday’s council byelection. “I’m all for Brexit. We should be looking after more of our own affairs. With Europe you’re losing your independence.” Party officials did not respond to interview requests for this article.

In Carrickfergus you don’t need to look hard for symbolism. The DUP’s local office is near a Norman castle and overlooks a 40-tonne Churchill tank planted on a lawn, its turret pointed at the Irish Sea – the sea in which the party will brook no regulatory checks lest they differentiate Northern Ireland from the rest of the UK. If that sinks any chance of a Brexit deal, so be it.

Warnings of economic pain in the event of no deal, and a restored hard border with the Republic, did not trouble Linda Kingston, 57, a retired personal assistant. “The country has been a mess and I think Brexit can open up new avenues for trade deals. I don’t see a problem with a border between north and south. We had one before.”

Such lack of concern causes heartburn in communities on the border, about 50 miles to the south, who remember army checkpoints, police fortresses and IRA attacks during the Troubles, and among diplomats in Dublin, London and Brussels who are tasked with averting a restored border.

The DUP was the only major Northern Ireland party that campaigned for Brexit in the 2016 referendum. About two-thirds of its supporters voted accordingly, an “uber-expression of Britishness” and longstanding Euroscepticism, said Jon Tonge, a University of Liverpool politics professor and author of a book about the party.

The party’s subsequent hardening approach to Brexit talks reflects not confidence but anxiety, said Tonge. “The notion of Northern Ireland being different is what started panic in DUP ranks. They’re perpetually fearful about being sold out by a British government.”

Ian Paisley, an evangelical Protestant preacher, founded the party in 1971 to stiffen unionist resistance to ceding power or influence to the Catholic nationalist minority, let alone the Dublin government, adopting a policy of “no surrender” and “never, never, never” over successive power-sharing initiatives including the 1998 Good Friday agreement.

After the DUP became the largest unionist party, Paisley performed a spectacular U-turn in 2007 by accepting the agreement and becoming first minister, with Sinn Féin’s Martin McGuinness, a former IRA commander, serving as his deputy at Stormont.

But there seems little prospect of the party changing course over Brexit. By equating regulatory checks with a border down the Irish Sea, the DUP has turned a potentially technical issue into a constitutional and therefore existential issue, with language to match.

Its leader, Arlene Foster, has warned the prime minister of “blood red lines”. An unnamed official told the Sun the talks were a battle over who blinks first – “and we’ve cut off our eyelids”. Another told Politico: “We are going to squeeze their balls until their ears bleed.”

Lurid terms that suggest little scope for compromise. “I don’t think they’re bluffing,” said Tonge. “They’ve dug in too deep and not given themselves enough wriggle room.”

The party has reached this zenith, its decisions carrying potentially momentous implications for the UK and the rest of Europe, on a flimsy edifice. It accounts for just 10 out of 650 MPs at Westminster and one out of 751 MEPs. Even in Stormont the DUP is a minority, holding 28 of 90 seats in an assembly that has not sat since a power-sharing administration collapsed almost two years ago.

In the 2016 referendum 56% of Northern Ireland voters wanted to stay in the EU versus 44% who voted to leave. Business leaders, including traditional unionists, have warned of grave economic damage from no deal or a bad deal. Polls suggest Brexit is fuelling support for a united Ireland, the DUP’s nightmare.

On top of this have come a stream of scandals, notably a bungled renewable heating scheme nicknamed cash-for-ash, which has exposed DUP dysfunction and alleged corruption – revelations that have alienated even core supporters.

A tarnished, minority voice on a small part of a small island, there could be something farcical about the DUP’s threats against vaster, more powerful forces – an echo of Monty Python’s knights who say “Ni”.

Yet Westminster’s unforgiving arithmetic, compounded by Sinn Féin’s refusal to take its seats, gives the DUP, for now, a mighty roar.

“The DUP do tend to mean what they say and say what they mean. It’s about sovereignty and culture,” said Nicholas Whyte, a Brussels-based expert on Northern Ireland elections. Apocalyptic headlines about a no-deal Brexit did not easily rattle a community that endured IRA bombs and bullets for three decades, he said. “The unionist community feels they have faced worse.”

Political polarisation further emboldens the DUP: no matter the scandals and the paralysed Stormont executive, no matter the potential costs and backfiring of Brexit, come election day many unionists feel they have no alternative but to stick with their tribe.

“We’re guilty of what everyone is guilty of – afraid of the other side,” said Allison Rea, 53, a credit controller, speaking on an esplanade in Carrickfergus overlooking the tank. She opposed Brexit but is a longstanding DUP voter. “It’s a fear vote.”