The de-facto deputy prime minister has warned that a no-deal Brexit could lead to the break up of the union.
David Lidington was speaking during a visit to a County Fermanagh bottling plant following a £20m investment.
He said the UK was now under greater strain than at any other point in his lifetime.
The cabinet minister said the threat to border businesses in the event of a no-deal Brexit cannot be understated.
Mr Lidington said the next prime minister needs to ensure that whatever happens the UK cannot leave the EU without a deal.
He also warned the threat to the union comes not just from Scottish nationalism or pressure for Irish unification, but from indifference amongst English opinion to the value of the union.
"There is a sense in which we take the union for granted," he said
Mr Lidington is responsible for ensuring good relations between the UK government and devolved administrations.
He regularly meets ministers from the Scottish and Welsh governments, and holds talks with key figures in Northern Ireland.