Any hi-tech solution to the problem of how to keep the Northern Ireland border open after Brexit is at least 10 years away, a leaked Home Office document has said.
The memo said the cost and complexity of using new technology to remove the need for border checks meant "the challenges of this work cannot be underestimated".
The finding will come as a blow to Eurosceptic Conservative MPs who have repeatedly insisted that technology could be used to keep the border open in the event of a no-deal Brexit, removing the need for the controversial backstop. Former First Minister Lord Trimble had backed an electronic border.
The memo, seen by Sky News, was drawn up by the Home Office's Policy Unit and sent to HM Revenue and Customs (HMRC) and the Treasury. It says there could be a possible technological solution but that it would come with a huge array of difficulties.
The solution would involve companies uploading data on goods and using blockchain technology, sensors and automated collection to pay tariffs.
The memo said: "If all these technologies are brought together, this could allow a seamless collection and analysis of the data needed. It would also provide the ability to target interventions away from the border itself."
But it also warned of a series of practical problems in introducing the technology, including cost, time and complexity.
It said: "The challenges of this work cannot be underestimated ... No government worldwide currently controls different customs arrangements with no physical infrastructure present at the border."
Warning that the technology would take over a decade to introduce, the document said: "Current realisation for a similar technological solution in the UK is 2030."
The memo also highlighted the cost and difficulty of implementing such a project and questioned whether the Government would be able to deliver it.
It said: "Any future system must operate with 28 government agencies and a myriad of interconnected existing and planned IT systems.
"There is currently no budget for either a pilot or the programme itself. And it will be expensive.
"This suite of technology would need to operate on both sides of the border; as such it would require agreement and commitment from Northern Ireland and the Republic of Ireland and possibly the EU, too. It is a big and complex project, with possibly tight deadlines.
"Government does not have the strongest track record on delivery of large tech projects."