When it comes to flashpoints in future EU-UK negotiations, there has been much focus on fish and financial services. But a more immediate concern looms when EU-UK talks open next month: the coming border in the Irish Sea. For the last few weeks, the two sides have been exchanging verbal warnings ahead of negotiations that will take place in an atmosphere that appears increasingly combustible. Boris Johnson has said that “emphatically” there will be “no checks” on goods flowing from Great Britain into Northern Ireland – an assertion the EU has, equally emphatically, rejected. Michel Barnier, the bloc’s chief negotiator, said checks are an “indispensable” consequence of the UK’s decision to leave the single market and customs union. Only by conducting the checks in the Irish Sea can they be avoided on the Irish mainland. “I understand the fears of negative economic fallout expressed by some about these checks, but Brexit unfortunately has consequences that we must manage,” Mr Barnier told an audience in Belfast last month. But in recent weeks, as the two sides have prepared for negotiations, there have been increasing rumblings in Westminster that Mr Johnson might not have been bluffing – and that the UK might actually not institute physical checks at the border. “Put it this way, it wouldn’t be a surprise if the UK didn’t rush to gold plate the Irish Protocol,” said a source familiar with the Johnson Government’s thinking. Rumours of a potentially hardline British stance have reached Brussels, where diplomats and officials are privately fretful about the implementation of the new border. Smith "pointed right at the elephants in the room" The sacking of Julian Smith as Northern Ireland Secretary on Thursday will have done nothing to inspire confidence that the British are fully preparing to implement their side of the bargain in a manner that meets EU expectations. Although not directly involved in Brexit negotiations, it was Mr Smith who persistently held the line against a no-deal Brexit last year while also questioning Mr Johnson’s original plan of reimposing a trade border in Ireland facilitated by technology – a plan that was rejected in Dublin and Brussels. At times during his tenure, Mr Smith did not mince his words. When Mr Johnson unlawfully prorogued Parliament in September, Mr Smith didn’t hide the fact that he had not been consulted from MPs. As court papers later showed, he made clear to Mr Johnson that the decision to prorogue risked leaving Northern Ireland rudderless in the event of no deal because legislation to enable the imposition of direct rule in the Province had not been passed. In October, when Brexit hardliners called for an end to security co-operation with the EU in order to try to force Europe to the table, Mr Smith took to Twitter to say that withdrawing co-operation was “unacceptable”. He was no less combative in private, according to a source who was frequently present at Cabinet during the May and Johnson eras. “With Brexit, in particular, there were always massive elephants in the room – but Julian was always the one who pointed right at them,” the source said. “He’d say very clearly: ‘That won’t work, that will end in disaster.’” Such truth-telling – amounting to disloyalty to the cause in the eyes of some Brexiteer colleagues – ultimately led to Mr Smith’s defenestration, despite the fact that he succeeded in restoring the power-sharing executive in Northern Ireland. That achievement won him plaudits from sources as diverse as the Irish Taoiseach, Leo Varadkar, and the DUP leader, Arlene Foster, this week – but it wasn’t enough to keep him his job. The question now being asked in Brussels and Dublin is what a total purge of the Cabinet ranks by Mr Johnson might portend as EU and British negotiators prepare to enter talks over the Irish Protocol. It was the agreement by Mr Johnson to create a customs border in the Irish Sea that ultimately unlocked the Brexit deal that had been agreed in October to much fanfare from both sides. Barnier: Northern Ireland "fallout" is coming What was given less detailed attention, however, was the cost of doing such a deal to the people and businesses of Northern Ireland. But, as Mr Barnier noted in his Belfast speech, the “fallout” is now coming. A leaked assessment from the Treasury during the election warned that requiring businesses to do customs declarations, documentary and physical checks would be “highly disruptive” to the Northern Irish economy. It said that costs on the high street would increase, employment in the retail sector would be hit and that border frictions would impose the equivalent of tariffs on about one third of all goods sold in Northern Ireland. Such “negative economic consequences”, as Mr Barnier termed them, are good reason for the British side to take a rather more laissez-faire approach to the required checks than the EU thinks is reasonable. Officially, the bloc remains confident that the UK will live up to its obligations under the Withdrawal Agreement but – just in case there was any doubt – Stefaan De Rynck, a senior Barnier adviser, reiterated the message on a visit to London last month. “We will not tolerate any backsliding or half measures,” he said, noting that the 11-month negotiation period would require “a lot of preparatory measures” so that the Irish Sea border would be operational on January 1 2020. Thus far, there is little evidence of these. The assumption among trade and industry groups is that the checks on goods flowing to Northern Ireland will be carried out at ports in Great Britain – Holyhead, Stranraer and Cairnryan – but the operators are still understood to be looking for clarity on how the border will operate. In part, this cannot be done until the Joint Committee set out in the Withdrawal Agreement meets to decide which goods are considered "at risk" of flowing south into the Republic of Ireland and therefore the subject of EU border controls. The precise nature of the controls will depend on the UK’s trade deal with the EU, but even a zero-tariff deal will still require checks for regulatory compliance and rules of origin content to qualify for that zero-tariff access. Goodbye to a voice of moderation? The implementation of the border has already proven to be a subject of intense interest among EU member states during seminars this month to discuss the implementation of the divorce deal. “Member states were making clear to the Commission that they wanted to be kept fully informed of how it was checking on the UK’s preparations for an operational border,” said a source with knowledge of the discussions. The concern among EU officials is that the UK will decide that such checks can be done in a "de-dramatised" way, on a risk-based basis, away from the border and without any new infrastructure at the ports. British negotiation sources said the Government does not dispute its obligations, which are enshrined in a jointly ratified international treaty, but added cryptically that there will always be discussion about "how zealously those obligations are enforced". With Mr Smith now relegated to the backbenches, the fear in Europe is that a proven voice of moderation in British politics has been stripped away – and with that, the risk of a serious clash over the Irish Sea border has just increased.