The “madman theory”, popularised by former US president Richard Nixon, involves scaring an opponent into concessions by cultivating an image of recklessness.
Mr Montgomery said the UK’s stance in the Brexit negotiations was becoming increasingly difficult to gauge and increasingly problematic for Brussels.
“Is the UK for real or is it not? Very hard to say,” he said at an event hosted by the Dublin Economics Workshop.
Is Mr Johnson adopting “a kind of Trumpian madman approach whereby he causes so much chaos that the EU will be forced to settle?” Mr Montgomery asked.
The UK plunged Brexit talks with the EU into crisis on Wednesday by explicitly acknowledging it could break international law by ignoring some parts of its EU divorce treaty.
UK ministers said the UK government’s proposed Internal Market Bill would ignore parts of the Withdrawal Agreement, which was only signed in January.
Mr Johnson was reported to have said back in 2018: “If Donald Trump was negotiating Brexit, he would create chaos right at the start of negotiations.”
While questioning the UK prime minister’s approach to negotiations, Mr Montgomery noted that Mr Johnson did broker a deal with the EU last year, albeit by accepting 95 per cent of what his predecessor Theresa May had negotiated and “backpedaling on the other 5 per cent”.
The Internal Market Bill, tabled in the House of Commons, states that “special regard” must be given to Northern Ireland’s place in the UK internal market and that there should be no new checks on goods moving from Northern Ireland to Britain.
But Mr Montgomery said the current UK administration had proven itself quite ignorant of some of the provisions laid out in the historic peace deal.
He also said the Republic had little choice but to adhere to the EU’s position “as the consequences of a no deal are so bad for us”.
“Clearly I imagine we’d be more open to fudges on various things than others but we can’t be going into a negotiation saying that.”
While there was cloud hanging over the negotiations, he said he believed there was more likelihood of a deal than not.
However, he said it was not inconceivable that the UK had decided it might be easier to crash out with no deal than to make compromises.