Shadow foreign secretary Lisa Nandy has accused Boris Johnson of being “missing in action” on the issue of border controls in Northern Ireland.

The Labour minister told Sky News the government must sort out the border in the Irish Sea which is “causing absolute havoc” and warned ministers they have a responsibility to ensure any kind of checks or disruption are minimised.

Her comments came as the UK’s Brexit minister warned Brussels that time is “starting to run out” to fix the problems facing Northern Ireland after Brexit.

On Sunday, Lord Frost said the UK government had “underestimated” the impact that the Northern Ireland protocol – part of the treaty which enabled the UK to leave the EU – would have.

In an article for the Financial Times before his upcoming meeting with European Commission vice-president Maros Sefcovic in London, Lord Frost – who was the PM’s chief negotiator during the negotiations with the EU, admitted ensuring the protocol worked had led to “political turbulence”.

“We underestimated the effect of the protocol on goods movements to Northern Ireland, with some suppliers in Great Britain simply not sending their products because of the time-consuming paperwork required,” Lord Frost said.

He added: “The EU needs a new playbook for dealing with neighbours, one that involves pragmatic solutions between friends, not the imposition of one side’s rules on the other and legal purism.

“But time is starting to run out. We need to see progress soon. I hope we can this week.”

Speaking to Sky News on Monday, Solicitor General Lucy Frazer also acknowledged the trade complexities surrounding Brexit and Northern Ireland are “more difficult than we anticipated”.

“It is very difficult on the ground in terms of trade. It is really important that we sort it and Lord Frost is doing just that.

“As it has panned out, on the ground it is more difficult than we anticipated and we do need to sort out that trade arrangement,” she said.

But over the weekend, new Democratic Unionist Party leader Edwin Poots said: “The Northern Ireland Protocol is bad for business in Northern Ireland and it is bad for every one of our citizens.”

He urged those “who want to make Northern Ireland work” to “speak with one voice against the absurd barriers placed on trade”.

Labour’s Ms Nandy also urged Mr Johnson to do more to resolve the issue as quickly as possible.

She told Sky News: “The prime minister made promises to the people of Northern Ireland that haven’t been kept.

“I think the best way to resolve this is through decent relationships, investing in those relationships and through pragmatism.

“We need to make sure we minimise any kind of border checks or disruption, and we can do that with good will on both sides.

“But there’s a feeling at the moment that the government is missing in action on this, particularly the prime minister.

“Boris Johnson has created this problem and yet he’s nowhere to be seen, I think there’s a real feeling of dismay about that, but he could turn that around.”

Meanwhile, former Brexit secretary David Davis said difficulties with the implementation of the Northern Ireland Protocol were inevitable after former prime minister Theresa May “conceded the so-called full-alignment wording”.

He told Sky News: “It was one of the things I resigned over you may remember.

“I did predict that the prime minister at the time, when she conceded the so-called full-alignment wording, that this was problematic, not what we were promised, and would lead to difficulties in the future – and that is exactly what we are seeing.”

Conservative Mr Davis added: “Once you’ve got to the point of agreeing the alignment of Northern Irish regulations with the south Irish regulations you are creating a border.

“Of one sort or another, you are creating a border which would end up falling in the Irish Sea.”

Mr Davis added that the issues “will be resolved” but that it is “an unnecessary difficulty” which “will add a couple of years of negotiation to the overall outcome”.