Daniel Hannan and Peter Mandelson not only disagree fiercely on Brexit, but both men believe that if the nation votes for their opponents on June 23 it will send a disastrous signal to Brussels.
Mr Hannan, a Conservative MEP and leading Eurosceptic, says that a Remain vote will be interpreted by the EU elite as an endorsement even by the UK for them to press ahead with European federalism.
Lord Mandelson, a former EU trade commissioner and outspoken supporter of ongoing membership, believes that a Leave vote will have pushed goodwill to the UK among other members states beyond breaking point.
The News Letter spoke to the two politicians in Belfast on Friday after they debated each other at a Manufacturing NI event at Belfast Harbour Commissioners, in interviews the first part of which we published on Saturday.
Reflecting on the prospect of a Remain vote, Mr Hannan said: “If we couldn’t get reform when we were about to vote on whether to leave the EU, as they see it we will have asked for fairly paltry changes, then failed to get them, and then voted for the status quo anyway. And then we’re going to say now give us some reform?
“Come on, they’ll laugh and they’ll be right to laugh.”
He added: “You can’t cast a qualified Remain vote, so vote Remain if you really like the direction the EU is going, but it will be taken as unqualified approval.
“The reaction in Brussels will be the Brits used to be the most sceptical and even they are now happy with unchanged terms so kiss goodbye to any reforms.”
Lord Mandelson, a former Secretary of State for Northern Ireland, sees things from almost exactly the other perspective.
“We are stretching people’s goodwill to breaking point,” he told the New Letter. “Look, Britain already enjoys a special relationship in the European Union, make no mistake about it.
“We have the strong economic partnership with Europe that serves us so well but we also have special safeguards for our national interests.”
He added: “That’s why I say if we vote to leave the European Union, the day after we do so that goodwill will evaporate.
“We will not get a deal that gives us anything like the same as what we have at the moment let alone better if we were to vote to Leave.”
Lord Mandelson dismisses the notion that the UK can easily strike trade deals with major countries such as China, with which he has long experience negotiating from his time as EU trade commissioner.
He said: “The whole economy is ringed by protectionism. You get through the protection and into the market and you’re facing every single regulatory hurdle, loophole, elephant trap in the world with China.
“So by all means, let’s over the next 20, 30, 40 years hope that China opens up a bit that if we can trade more with China and India for that matter and Brazil for that matter ... there are a whole lot of countries in the world with whom we can do more trade but they ain’t open yet.
“In the meantime we don’t have to look to those countries instead of our home market in Europe. We do more business in Europe, our businesses grow and become stronger and more competitive big in Europe and in time bigger in the rest of the world.”
But Mr Hannan is confident about Britain’s trading position outside the EU.
He envisages “a pan European free trade area, a lightly but effectively regulated common market that goes from Iceland and the Faroe islands to Turkey and Armenia, has 50 states and territories in it and regulates the markets, institutions”.
He added: “Then within that you have a much tighter group of countries with a single currency, single foreign policy, single president, police force, army, all the things they want.
“Doesn’t that leave everybody happier?”
Mr Hannan said: “I had hoped that David Cameron would be able to deliver at least a route to that.”
Click here for the final part of Mr Hannan and Lord Mandelson’s interview with the News Letter, discussing Brexit and nationalism within the UK