The Brexit secretary has hinted that the government could amend its proposal to give the Democratic Unionist party an effective veto over its plan for an alternative to the Irish backstop

With EU leaders not willing to accept the UK’s ideas and talks between the two sides suspended over the weekend when Boris Johnson had been hoping to intensify them, Stephen Barclay said on Sunday that the government would be willing to discuss changes to the mechanism designed to ensure the new arrangements receive political approval in Northern Ireland.

He also sounded open to possible further movement on customs, saying the UK was willing to discuss the detail of how its plan might work.

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In rhetorical terms the government has shifted considerably from what it was saying just before it published its plan for an alternative to the backstop on Wednesday, when it was insisting this would be its “final offer” to the EU.

But the gap between the two sides remains considerable, and Barclay’s emollient language may be motivated as much by a desire to deflect accusations that the government is being unreasonable as by any serious expectation of a deal being reached before the EU summit starting on 17 October.

Under the UK plan, Northern Ireland would remain in the EU single market for goods after Brexit but in the UK customs territory. This arrangement, intended to avoid a hard border between Northern Ireland and Ireland, would depend on the Northern Ireland assembly voting for it, and continuing to vote for it every four years.

One objection to this is that the assembly is currently suspended. Another is that, under the “petition of concern” mechanism used for contentious issues in the assembly, votes have to be agreed not just by a narrow majority but with the backing of a significant block of both unionist and nationalist assembly members. In practice this means the main unionist and nationalist parties, the DUP and Sinn Féin, can exercise a veto.

Quick guide Why is the Irish border a stumbling block for Brexit? Show Hide Counties and customs Inside the EU, both Ireland and Northern Ireland are part of the single market and customs union so share the same regulations and standards, allowing a soft or invisible border between the two.

Britain’s exit from the EU – taking Northern Ireland with it – risks a return to a hard or policed border. The only way to avoid this post-Brexit is for regulations on both sides to remain more or less the same in key areas including food, animal welfare, medicines and product safety. The 'backstop' in Theresa May's Withdrawal Agreement was intended to address this - stating that if no future trade agreement could be reached between the EU and the UK, then rules and regulations would stay as they are. This has been rejected by Brexit supporters as a 'trap' to keep the UK in the EU's customs union, which would prevent the UK striking its own independent trade deals. There are an estimated 72m road vehicle crossings a year between Northern Ireland and the Republic of Ireland, and about 14% of those crossings are consignments of goods, some of which may cross the border several times before they reach a consumer. Brexit supporters say this can be managed by doing checks on goods away from the border, but critics say it will be difficult to police this without any physical infrastructure like border posts or cameras, which could raise tensions in the divided communities of Ireland.

Interactive: A typical hour in the life of the Irish border Photograph: Design Pics Inc/Design Pics RF

The No 10 plan envisages the assembly having to vote for Northern Ireland joining the EU single market for goods, meaning the vote could only be won with DUP support. If the default were for Northern Ireland to be in that arrangement, only exiting if the assembly voted to leave, then in practice it would be Sinn Féin that had the veto.

On Friday Julian Smith, the Northern Ireland secretary, was told by some of the non-DUP parties in Northern Ireland that what was being proposed was a non-starter.

One source with knowledge of the meeting said: “The message has gone back from all quarters in Northern Ireland, from Sinn Féin to the Traditional Unionist Voice, that this is unworkable and it will destabilise the institutions and the Good Friday agreement and is not plausible – and in light of that, if [Smith] is serious about getting a deal, he has to come back with something more realistic.”

On Sunday, in an interview on the BBC’s The Andrew Marr Show, Barclay indicated the government might consider moving on this. Asked if he was willing to change the system being used to ensure the new arrangements had the backing of the people on the island of Ireland, he replied: “The key issue is the principle of consent.

“Now, the mechanism – we’ve set out proposals in our legal text. We can obviously, as part of the intense negotiations in the coming days, discuss that mechanism.”

Barclay was also asked if the UK would shift on its plans for minimal customs checks, away from the border, on goods travelling between Northern Ireland and Ireland. These are currently unacceptable to EU leaders who complain they are too vague and that they would in practice fail to protect the integrity of the single market and the customs union.

Asked if the government was willing to compromise further on customs, Barclay said: “We’ve set out a broad landing zone. In the detail of the negotiations, of course we can get into the detail as to how operationally they work, what legal certainty is required by the commission.”

In public ministers have sounded relatively conciliatory in recent days, while also stressing that the UK will leave the EU on 31 October despite parliament having passed a law, the Benn act, intended to stop a no-deal Brexit. In private government sources have been briefing that the prime minister might subvert the act, and even try ignoring a vote in parliament for him to be replaced by someone else as leader of an interim government.

Asked if Johnson would comply with the Benn act, which requires him to write to the EU by 19 October requesting a Brexit extension if no deal has been agreed by then, and if MPs have not voted to authorise no deal, Barclay replied: “I can absolutely confirm that the government will abide by the law. The prime minister is clear on that.”

Asked if that meant he would send the letter, Barclay said: “Whatever the law says, we will comply with the law.”

But Barclay sidestepped a question about why a “senior No 10 source” told the BBC that Johnson was not prevented by the Benn act “from doing other things that cause no delay”, including sending messages to EU countries intended to persuade them to reject an extension.

In a separate interview on the Andrew Marr Show, Shami Chakrabarti, the shadow attorney general, said Johnson would be acting unlawfully if he did this.

“If you send the letter, as you are required to under the law, and then seek to undermine it by other means, you have not kept faith with the law. You have not fulfilled your specific statutory duty to seek an extension. That would be unlawful conduct,” she said.