Sir Ivan Rogers, Britain’s former top diplomat in the EU, said he warned the pair in autumn 2016 that a desire to please Brexiteer Tories, Northern Irish unionists and Ireland had led the government into an untenable position.
May, who had come to power in July 2016 after David Cameron’s resignation, was underestimating the Irish border issue, which would “obviously” be at “the core” of the problem of delivering Brexit, he said.
Her pledge to avoid new border posts between Ireland and Northern Ireland, while keeping Northern Ireland in lock-step with the rest of the UK and to leave the customs union, were undeliverable at the same time, said Rogers.
May’s red lines in the end led to the Irish backstop, which turned Brexiteer Tories against her deal because they believe it will trap the UK in the EU’s close orbit via a de facto customs union.
Johnson and his leadership rival Jeremy Hunt have now pledged to try and get the EU to junk the backstop, which Brussels is likely to refuse, leaving Britain edging closer towards a no-deal Brexit.
Rogers, who quit in early 2017 as Britain’s permanent representative to the EU over differences with May, suggested the PM had been storing up trouble by making conflicting promises.
“The Irish question was being underplayed,” he told the Commons foreign affairs committee.
“We were not focusing enough on it.
“And it was obviously going to be the core of the problem.
“I do think one of the more unpopular things I said to the prime minister in the autumn of 2016 was you’ve made three commitments in good faith to different audiences but they are not really compatible with each other.
“You’ve said to the Irish under no circumstances will a border be erected across the island of Ireland.
“You’ve said to the democratic unionist community under no circumstances will there be divergence from the rest of Great Britain.
“And you’ve said to the right of your own party that you are heading out of the customs union.
“You can’t do all three, you’ve got to choose two of the three.
“And I had the same conversation with the then-foreign secretary as well.”