Once again the European Union is having to weigh up the impact of a new British prime minister on the Northern Ireland Protocol negotiations.

While there was widespread relief that Boris Johnson did not make a return to Downing Street, officials and diplomats are keeping their counsel over Rishi Sunak.

They are measuring his natural caution against his longstanding commitment to the Brexit cause, and whatever debts he might owe to the hard right European Research Group (ERG) within a still fractious Tory Party.

Brussels and Dublin are also mindful of how ruthlessly the bond markets punished his predecessor Liz Truss's reckless economic gamble. They calculate that a hard confrontation with the EU over the Protocol, leading to a potential trade war, will not be in Mr Sunak’s interest.

"If anything is known about Sunak it’s that he is both meticulous and he is cautious," says a senior Irish official.

"Given his predecessor’s demise, he will be very carefully reading the signals from the markets. That would tend to argue against a big confrontation with the EU and it would exacerbate divisions in his party as well. So it’s hard to see why he’d want to go there. But let’s see."

An EU diplomat says: "Sunak is clearly somebody that understands the markets. He was right about Liz Truss’s economic plans from the get go. We've also seen what the markets think of Brexit, so perhaps that might also have a moderating effect."

The view in capitals is that Mr Sunak will prioritise restoring confidence in the British economy, and start to acclimatise voters to the pain that will be inflicted through higher taxes and spending cuts.

"Finding the right balance in his cabinet and restoring the confidence of the markets in his government are probably more important than dealing with Northern Ireland or the EU," says a senior EU diplomat.

In contrast to Ms Truss, who centralised the handling of Protocol negotiations, Mr Sunak is expected to delegate so he can concentrate on the economy.

EU diplomats are trying to ascertain whether Mr Sunak's Brexit enthusiasm will be eclipsed by pragmatism

Member states will look for early signals that the talks, which had just resumed under Ms Truss, will continue towards a positive trajectory.

Mr Sunak has kept foreign secretary James Cleverly, Northern Ireland Secretary Chris Heaton-Harris and Minister of State Steve Baker in their posts.

"That's helpful," says the EU diplomat. "It means not another about face and having to rebuild relationships with people on the other side."

Northern Ireland Secretary Chris Heaton-Harris was kept in his post

It will also have been noted that Mr Sunak arranged early phone calls with the European Commission president Ursula von der Leyen and Taoiseach Micheál Martin. Downing Street said that in both calls Mr Sunak expressed a preference for a "negotiated settlement" to the sticking points around the Protocol.

That in itself does not provide too many clues.

Ms Truss used similar language with the caveat that if a negotiated outcome was not possible she would press ahead with the Northern Ireland Protocol Bill (NIPB), which would unilaterally demolish the Protocol.

Mr Sunak has long been a convinced Brexiteer and as Chancellor he approved of the NIPB, voting for it in the third reading in the Commons. He told Bloomberg in May that the way the Protocol was operating posed challenges to "stability" in Northern Ireland.

However, Mr Sunak was a constraining voice at Cabinet when Boris Johnson, urged on by former Brexit negotiator David Frost, pondered triggering Article 16 and going for confrontation.

'A Brexiteer at the end of the day'

EU diplomats are trying to ascertain whether Mr Sunak’s Brexit enthusiasm will be eclipsed by pragmatism - with one eye on the markets - or whether any promises he made to the right wing, in order to actually win the contest, will leave him beholden to the ERG.

"Sunak is a Brexiteer at the end of the day," says another EU diplomat.

"On the other hand, he was always the voice of moderation at Cabinet. [Former Treasury permanent secretary Tom] Scholar helped a lot too. The problem is, what did Sunak promise to the eurosceptics in his cabinet and the ERG in order to keep them quiet? His election was an extremely smooth ride. People, whom you would have assumed would have been in the anti-Rishi camp, let it go. We don't know what he promised them."

EU diplomats are trying to ascertain whether Mr Sunak is beholden to the ERG

A hint came from ERG spokesman Mark Francois MP, just hours before Mr Sunak was acclaimed leader of the party.

He told reporters in the House of Commons that the ERG had been unable to choose collectively between Mr Sunak and his remaining rival Penny Mordaunt (after Mr Johnson pulled out), but both candidates "were equally adamant that they would take… a very robust line on the Northern Ireland Protocol, up to and including, if necessary, utilising the Parliament Act to ensure that the Northern Ireland Protocol Bill reaches the statute book."

In other words, if the Lords were to delay passing the Bill, Mr Sunak promised the ERG that he would use the Parliament Act to prevent that happening and to get the Bill enacted.

That might have been an easy promise to make since it looks like the Lords will amend the bill rather than delay it.

There has been no rupture to the encouraging mood music since the beginning of September but we have yet to get into the weeds of where both sides are going to move in order to give the negotiations momentum.

During the second reading of the Bill on 11 October, out of 60 Lords who spoke 40 were opposed to the Bill, while 20 sided with the government. But there was little support for delay mechanisms.

That is not to say the Bill won’t be heavily amended. "It's obviously going to have a really heavy time getting through the Lords," says one peer.

Those amendments could include a requirement for Mr Sunak to live up to the UK’s international treaty obligations.

During the debate Lord Kinnoull, the crossbench chair of the European Affairs Committee, emphasised the "sanctity" of such obligations.

"As the UK has assumed such a leadership position in the current war in Ukraine," he told the Lords, "the most common comment made to me is of the importance of the UK especially showing leadership in living up to the spirit and letter of international agreements."

The House of Lords chamber

There are other elements to the bill which could be amended: the fact that it gives ministers sweeping powers to unilaterally alter part of an international agreement without parliamentary scrutiny, and the need to be even-handed in dealing with matters relating to the Good Friday Agreement (GFA).

"I would expect the bill, were it to go through the Lords, will be very heavily amended with very big majorities on all those points and a few others as well," says Lord Kinnoull.

However, as one member of the Lords points out, Boris Johnson has elevated over 100 new peers to the upper chamber, not all of them Tories but enough to blunt any moral force that amendments to the Bill might bring.

"It's very evident when discussing anything to do with Europe," says the peer, "that there are now a lot more of them who are prepared to stand up and speak. And of course they take the whip."

For the amendments to win the support of the Lords, they will require the votes of Crossbench peers - who are not subject to a party whip - and Labour members. It is not yet clear how they will vote.

If the amendments are carried, then the Bill goes back to the Commons and it is most likely that Mr Sunak’s government will vote against the Lords’ amendments by inserting their own amendments.

Protocol 'ping pong’

These will then go back to the Lords for what is called "ping pong". In that situation, the Bill stays alive in the Lords and attracts a sizable amount of coverage, but a government with a big Commons majority will win out in the end.

The high point of Lords recalcitrance was the Brexit Withdrawal Bill in the final months of 2019, after the EU and UK had concluded the divorce treaty.

On that occasion the House of Lords had approved five amendments to the bill during the ping pong phase, only for Boris Johnson’s government to overturn all of them by late January 2020, including, controversially, an amendment by the Labour peer Lord Dubs recommending the right of unaccompanied child refugees to be reunited with their families in the UK.

Peers will not start voting until report stage, which will not happen before 21 November. Given that votes in the House of Lords happen on Mondays and Wednesdays, it seems likely that the ping pong process would normally continue until January before gaining royal assent.

The interplay between the ongoing negotiations over the Protocol and the Bill’s passage through the Lords and back and forth to the Commons will be key.

Will Mr Sunak's vaunted new integrity and professionalism include abiding by treaties the UK has signed, and a rethink on a zealous, ERG-approved bonfire of EU retained law?

EU capitals will be watching closely to see if Mr Sunak, whatever promises he has made to the ERG, signals any intent to slow down the progress of the Bill. EU diplomats have made it clear that if the Bill becomes law while the negotiations are continuing it will change everything.

"With Truss there was a sense that the Protocol bill wouldn't be taken off the table, but that they wouldn't push it and progress it either," says one EU diplomat.

"It wasn't made explicit, rather it was between the lines. It’s not all that the EU wanted but it's something. With Sunak, it's too early to tell where he stands. But that would be a key signal for our side of the channel."

There has certainly been no rupture to the encouraging mood music since the beginning of September. But we have yet to get into the weeds of where and how both sides are going to move in order to give the negotiations momentum.

Officials are not yet at the point where they can indicate which issues are revolved and which remain outstanding

According to multiple sources, the atmosphere in the technical talks which resumed in mid-September has been positive, with some progress being made on the low-hanging fruit of VAT issues, tariff rate quotas (on steel), and on the integration of data systems covering the movement of goods from GB to Northern Ireland.

Technical teams have been working both in Brussels and London each week to an agreed timetable focussing heavily on the movement of goods, customs, state aid, and both Mr Cleverley and his EU counterpart Maroš Šefčovič are due to speak "regularly" with continuity the order of the day, according to one official.

However, officials are not yet at the point where they are colour-coding individual bits of text red and green, indicating which issues are resolved and which remain outstanding, in anticipation of an endgame.

"On the [UK’s] red and green lanes [proposal], they're still very far apart," says one EU diplomat briefed on the talks. "So, it's a mixed bag. We've been talking a lot about mood music over the past couple of weeks, even with Truss in place. The mood music is still good, but on substance there's nothing to report on the issues that matter."

A senior Irish official adds: "The talks haven't really gotten very far at all. Truss’s time in office was so turbulent that nobody really felt they had the mandate to move on anything, or to engage deeply on anything."

'Integrity, professionalism and accountability'

In his first speech at the lectern in Downing Street, Mr Sunak clearly and quickly drew a thick line between him and the daredevil populism of his two predecessors.

His government, he said, would have "integrity, professionalism and accountability at every level," while his remark that the 2019 electoral mandate did not belong "to any one individual" was a clear rebuke to Boris Johnson.

Will this vaunted new integrity and professionalism include abiding by treaties the UK has signed, and a rethink on a zealous, ERG-approved bonfire of EU retained law?

Mr Sunak had boasted during the summer Tory leadership contest, complete with a video showing stacks of "EU regulations" being fed into a shredder, that he would repeal or review 2,400 pieces of post-Brexit EU laws "within 100 days" of taking office.

ERG spokesman Mark Francois told reporters that Mr Sunak would take 'a robust line' on the Northern Ireland Protocol

According to the Financial Times, his officials have conceded that that is not going to happen, nor would there be a Brexit Opportunities Minister.

Will this new sobriety extend to the Northern Ireland Protocol?

It could cut both ways. On the one hand Mr Sunak may feel that he does not need a trade war, or trade irritants, with the EU when every fibre of the new government will be about restoring economic credibility.

On the other hand, if Mr Sunak has deprived Brexiteers of the red meat of purging leftover EU regulations, and the promise of glittering Brexit opportunities, he may feel he has only one sphere left in which to placate the right wing of his party - the Northern Ireland Protocol.

"We'll be watching the early signals out of London as to whether he wants to get [the Northern Ireland Protocol issue] out of the way," says a senior Irish official.

"If he does, there is a willingness to help with it. But if he doesn’t, we're just where we were."