Negotiating parties always posture outside the room and get on with the business inside. When it comes to Prime Minister Theresa May and her European Union (EU) counterparts, fighting talk is not what we need – it is fuelling feelings of nationalist protectionism both sides of the channel.

I want to ask the politicians a favour: stop trying to show your own electorate that you are doing a good job by talking down the opposition and playing to the crowd.

Take a leaf out of Anthony Joshua's book on how to go into a fight. Refuse to say nasty things about your opponent. Do your talking in the ring.

This is the real problem with patriotism, it relies on something heady and irresistible for a politician: a common national enemy. If we are not careful our leaders will be forced to make us hate one another so that they can win elections, or simply get on with their jobs.

I used to be an innocent internationalist, free from the furious passions of patriotism, right up to the moment that I heard that the HMS Sheffield had been hit by an Exocet missile.

The news crossed the Atlantic to the US where I was working as a scientist. Surrounded by bemused Americans, I unfurled my Union Jack and put it on display, ready to wave in the face of the Argentines. I was ready to see enemy soldiers blown up and killed.

I had previously thought the Falkands War was truly daft. But once I got going I was pumped about wiping the Argentinians out, showing them what Britain could do. Then I caught sight of my own reflection and I realised, not for the first time, that the urbane international Burnett needed careful supervision.

We are all slaves to our passions for sure. I did, however, manage to pull myself back together and see why it was good to keep the angry me in check.

After the initial roar of patriotism, other images tempered my instincts. I saw a badly wounded Welsh Guard arriving by train at my hometown. It was like learning those lessons of conflict written down in First World War poetry.

And the year after the conflict I had a long discussion with an Argentine colleague in the US who told me what a good idea the war had been given what an awful man General Galtieri was. I had not known that young men's lives were caught in the middle of internal opposition, nor what complexity and political distraction was at play.

Sensible, calmer thoughts took over the jingoistic ones but it was still the most awful of warnings. Why had it been so easy to fan the flames of nationalism? I now knew that my supposedly deep love of 'other people' needed some care before it happened again.

And it has just happened to me again. I was a 'Remoaner', an instinctively internationally-minded EU-loving metropolitan elitist, free from prejudice of the rest of Europe, right up to the moment when I heard EU Council President Donald Tusk telling my country what it could and couldn't do.

And in that moment I realised just how nasty this is going to get. I knew it because I felt my patriotic furies re-engage. I could not help but feel the old embers of hate, and the desire to silence this Polish-accented bureaucrat.

Despite the deep respect and love I have for a lifetime of continental academic colleagues, teachers and friends, nationalism lies nearer to the surface than we convince ourselves. Not just in the extreme-Brexiteers –but in us all.

Of course, I did subsequently calm down. But we are kidding ourselves if we don't think that our patriotic instincts can override rational debate in a moment – and indeed silence it in anger.

And then on Sunday (30 April) morning as I was listening to US National Public radio, the Tusk's words rang again in out in the kitchen. Don't react, I said to myself as I just about kept cool. But that man was telling America what the UK could and couldn't do. It felt intolerable. I felt attacked and my adrenalin surge.

So I tried telling myself that this is all part and parcel of negotiation, that there will be calm and sensible discussions inside the room. I know it is like that as I have led negotiations myself in China and India.

But this time, it is much more dangerous than that. The words spoken outside will drive people to look at people in their own community and feel differently about them. Division will deepen, trenches will form.

Keeping mum in public

Words spoken about outrageous claims and delusional behaviour will backfire not on the people inside the room but those of the 'other' that have to live among us during the negotiations. So I need to ask a big favour of the politicians. Shut up. Yes: Shut up.

We want to know that our elected politicians are doing a good job in negotiating with Brussels but let's try not to ask too much. Like her or loathe her, we should cut Theresa May some slack – this is no time for the UK to relive Elizabethan speeches as we set out to fight the Armada. We need wisdom, not just a Warrior Queen.

And can I ask this of my other European neighbours too. Cut the European Commission some slack. We don't need the continent to channel Jean d'Arc to our Britannia when we should be thinking about jobs, about opportunity and peace.

And the cost of this will be far greater than money. Remember all the Brits living across Europe and our dear children who live among people who could come to hate them. Remember all the Europeans and their dear children living among us who we must, for our own and our children's sake welcome amongst us.

There are precious few flags for cooperation. Few marches for compromise. Few battle hymns for the common good of a continent at peace which was once fractured, unstable and prone to war.

But if you don't think risking this is a problem and you want to bash the hell out of our neighbours, then the furies have already got to you. And after the fire of battle will come what always follows, the reckoning of loss. For the sake of our future, we need to conquer our own unchecked instincts and to measure patriotism with wisdom. If we can't do that, we need to start praying.

Professor Sir Keith Burnett CBE is the Vice-Chancellor of the University of Sheffield and President of the UK Science Council.