A £355m government-funded support service designed to help British businesses deal with post-Brexit trading arrangements for Northern Ireland is failing to provide traders with basic answers to questions, MPs were told on Wednesday.

The complaints from frontline users of the Trader Support Service (TSS) came as the UK and the EU prepared for critical talks on Thursday to resolve mounting issues with the Northern Irish Protocol that has caused growing political tensions.

The British government is demanding that the EU extend grace periods designed to ease the implementation of the protocol, which Boris Johnson agreed as part of the Brexit withdrawal agreement.

The deal requires all goods flowing from Great Britain to Northern Ireland to comply with onerous regulations under the EU customs code, creating a trade barrier down the Irish Sea that divides the UK internal market, riling pro-Brexit Tories and leading Unionists.

Michael Gove, the Cabinet Office minister responsible for the protocol’s implementation, has demanded an “urgent reset” of the deal, including permanently reducing bureaucratic barriers hampering the movement of pets, plants and food products to Northern Ireland.

Gove is to meet his EU counterpart Maros Sefcovic in London on Thursday after days of tense exchanges.

Gove on Monday warned that the EU’s “integrationist theology” undermined peace in Northern Ireland, drawing a sharp response from EU diplomats.

EU diplomats said Sefcovic would look to diffuse tensions and find solutions to individual problems within the existing legal frameworks of EU customs rules, but would not agree to blanket exemptions to the protocol.

Port and logistics operators told the Commons’ Northern Ireland Affairs Committee that the protocol had caused market distortions, lower trade volumes and service disruptions as traders struggled to deal with the additional red tape.

The complaints about the TSS — a consortium of customs clearance operators led by IT company Fujitsu formed to provide free assistance to traders — came a month after trade groups warned it was “simply not good enough”.

Stephen McAneney, managing director of logistics group Allied Fleet Services, said there was “no consistency” in the information coming from the service and advice was confusing and conflicting.

“You can phone in and speak to one person and they can give you an answer, and then you’d go away, think about it, then phone back in and get completely the reverse answer,” he told the committee.

Sarah Hards, business development manager at AM Nexday, a retail distributor in Larne, said there was an apparent lack of training among staff who were “pleasant” but often appeared to have “no previous experience” in customs and logistics.

“They really sometimes fail to grasp what you’re talking about even after a long conversation,” she added.

Witnesses from the shipping and logistics industries backed Gove’s demands for more time, including extensions to grace periods, to adapt to rules which are due to come into full force on April 1.

“What I see is huge market distortion currently taking place on a big, big scale,” said Ian Davies, the head of UK port authorities for Stena Line, adding that freight flows had halved from Holyhead to Dublin as supermarkets switched to Scottish routes.

Nick McCullough, the managing director at DFDS Northern Ireland, a shipping line, said turnover for January was 23 per cent down on last year, adding that flows were improving but more slowly than expected. “In a low-margin business that cannot go on for too much longer,” he warned.

The Cabinet Office did not return a request for comment at the time of publication.