Dr Liam Fox is a former Defence Secretary and is MP for North Somerset.

There are a number of things about this referendum that should not have come as a surprise to us. Powerful passions were bound to be aroused in such a fundamental constitutional debate and, given the nature of our political system, and the fact that the Conservative party seems more engaged with the process than any other, a number of blue on blue clashes were unavoidable. What was avoidable is the situation where personal attacks, on integrity, honesty and motives have become more and more common and are detracting from some of the key substantial elements of the debate.

I have always believed that the issue of the European Union held an existential danger for the Conservatives and I told the Prime Minister some years ago that I believe there was a 30 per cent chance that the Conservative Party might break on this issue sometime in this decade. My underlying reason for this is that in the Conservative Party, this whole issue is not simply about how we organise our affairs, but goes to the very heart of the issue of democratic accountability itself.

I want to leave the European Union for three reasons; I want to be able to regain control of our own laws and be able, through the ballot box, to throw out the lawmakers with whom I disagree; I want to have control of our borders and determine who settles in the United Kingdom; and I want to have greater financial freedom, unrestricted by EU interference and unencumbered by our net contribution. All of these issues should provide us with sufficient grounds for a full and substantive debate in the days before June 23, without resorting to the deeply personal campaigning we have seen in recent days.

Why have we found ourselves in this position? Certainly, given that David Cameron has said that he would stand down before the next election, it was inevitable that there would be an element of leadership beauty contest mixed in with the campaign. To think otherwise would be to take naïveté to an art form. Perhaps we simply find it too difficult to break ourselves out of the general election mindset where attacks on leading opposition figures are the norm and a way of diminishing their overall credibility. Yet we have to constantly remind ourselves that this is not a general election and how we behave towards one another will have potentially momentous implications.

It is not just the nature and subject of the debate itself which poses a danger to the Conservative Party but the fact that we are in office and, thanks to the Fixed-term Parliaments Act, will be there until May 2020. We have always known that it would be a difficult task to come together and put aside our differences after the referendum, whatever its outcome, but a complex challenge is now turning into a Herculean one. Mutual respect, self-discipline and careful language are all possible within a contentious debate, even one as explosive as our membership of the EU.

Those who say that they want to win the referendum “at any price” need to consider what “any price” might actually mean in terms of our ability to govern our country well. Take, for example, John Major’s interview on the Andrew Marr show on Sunday. It is, or would have been, perfectly reasonable to say that he did not believe that the money saved from Britain’s budgetary contribution would all find its way to the NHS. It would be, after all, a decision taken by the British Government by the normal process of collective responsibility. What I found disappointing, not least as someone who holds him in the highest personal regard, was the very personal nature of the attacks. To say that the NHS was “about as safe with them [Michael Gove and Boris Johnson] as a pet hamster would be with a hungry python” and then that “Michael Gove wanted to privatise the NHS, Boris want to charge people to use it” will undermine the credibility of two senior Conservative politicians on the NHS for a long time to come.

Likewise, it is perfectly obvious that the Prime Minister will never be able to control EU migration if we remain in the EU and that our election promise to reduce migration to the “tens of thousands” is unachievable. That statement of fact is, however, very different from saying that the “Prime Minster cannot be trusted” on immigration. Too much ammunition for our political opponents is being handed to them on a plate and even an Opposition as hapless as the current one can be expected to use it. Today’s blue on blue attacks will soon morph into red on blue attacks and we will have handed them the bullets. Add to all this what is likely to be a sustained attack on Treasury credibility, given their ludicrous claims to be able to predict the effect of Brexit 60 quarters in advance and it is easy to see where we may be creating difficulties for ourselves in the future.

I am totally convinced of the case for leaving the European Union on economic, democratic and security grounds. I see no need to personalise the attacks to persuade the British people that they should take control of their own destiny on 23 June. If the remain campaign are equally confident then they should make their case positively for the benefits of remaining in the European Union. Personal attacks will only create long-term bitterness and make our ability to come together more difficult. I want to leave the European Union, but I also wants the Conservative party to survive as the natural party of government in a free United Kingdom. We all have a duty to behave responsibly in the coming weeks. It’s time to take a deep breath, to cool it, and to stick to the issues.