The Chief Constable of the PSNI has said he feels "in the dark" as he attempts to prepare his service for Brexit.
George Hamilton told the Northern Ireland Committee that, just nine months before the UK leaves the EU, he has a business plan, but no-one to present it to.
"We can't deliver the full business case until we know who is co-ordinating this," he said.
"We do feel a little bit isolated and an orphan in this."
Mr Hamilton pointed out that HM Revenue and Customs have had an uplift of 4,000 officers and the Border Force of 2,000 in preparation for Brexit.
"I have asked the question, could we see beneath the structure of their business case to help us to inform ourselves of what it is we need to present," he said.
"With the lack of a nominated person, either a senior official or a minister, to say I'm taking responsibility for co-ordinating all of these difficulties and challenges, operational and strategic and constitutional, around the border issue in the post-Brexit scenario, we feel like we are in the dark around all this.
"We don't have that go to co-ordinator to assist us, to help us navigate our way through it."
Assistant Chief Constable Stephen Martin also appeared before the committee, and warned there are far fewer police at Northern Ireland's air and sea ports than elsewhere in the UK.
"Those officers are going to be critically important. We are under-resourced in those, we have been under-resourced for some time.
"We have identified it, we have prepared financial cases, we have submitted them to Government, but we are not getting the outcome we want," Mr Martin told the MPs.
"And when I say we are under-resourced, we are under-resourced by at least half per million passengers, than Wales, or in the North East, Newcastle."
Mr Hamilton said the PSNI has produced a "stock-take" in the "absence of clarity".
The main issues identified in the paper include how tighter immigration controls can be created while maintaining the common travel area, ensuring criminals and terrorists do not exploit the border, and avoiding a hard border.
"If it's not going to be physical infrastructure at the border, does that mean increased compliance checking, increased enforcement activity?
"And if it does, where are those people going to come from, are they going to drive from Belfast or Coleraine every day, or does it make sense to have some sort of accommodation spread at strategic points across the border?"
Turning to force strength, Mr Hamilton said he needed an extra 400 officers.
The Chief Constable said police officer numbers currently stand at 6,600, but he needed closer to 7,000 officers to deal with Brexit on top of legacy issues and the current hostile policing environment.
Earlier this month, the EU's chief Brexit negotiator, Michel Barnier, said the UK will be kicked out of the European Arrest Warrant after it leaves the UK.
The warrant allows EU members to request the arrest and detention of criminals in other countries without extradition talks between them.
Mr Hamilton said: "The European Arrest Warrant and biometric data, all of that needs fixed, and there is a real operational impact for us if we don't have a transitional period or some parallel bilateral mechanism to deliver the same thing."
Meanwhile, the Chief Constable also warned that Brexit has the potential to cause public disorder.
"There is also a further potential impact which we wouldn't want to talk up, but we also think it would also be remiss of us if we didn't mention - the fact that Brexit could cause some communities to feel that their sense of identity is under threat," he said.
"From our engagement with people in communities along the border and elsewhere, there is potential that this issue could raise community tensions, people could feel less secure and more vulnerable about their own identity as a result of Brexit.
"And, of course, in the past we have seen that manifest itself sometimes in street disorder and difficult policing scenarios."