Iain Duncan Smith fears damage to the Conservative party beyond EU referendum

Iain Duncan Smith, the government minister for Work and Pensions, has said the Prime Minister is not being "respectful" to his colleagues, and that his campaign to remain in the EU has "become characterised by spin, smears and threats". He also stated that he has concerns that the damage being done inside the Conservative party may have consequences beyond the referendum. The remarks represent the most clear sign so far of the growing tension in the Conservative party over the possibility of Brexit.

Iain Duncan Smith today delivers a devastating attack on the 'spin, smears and threats' being deployed by the Government machine to 'bully' Britain into remaining inside the EU.

Writing in today's Mail, he said a series of 'highly questionable' dossiers churned out by Number Ten and the Foreign Office had threatened the public with 'almost Biblical consequences' if they dared to vote to leave.

And he warns of lasting damage to British politics beyond the June 23 referendum if David Cameron and the other leading players in the Remain camp do not conduct the debate in a more 'respectful manner'.

Iain Duncan Smith is attacking the 'spin, smears and threats' being deployed by the Government machine to 'bully' Britain into remaining inside the EU

Two weeks after the Prime Minister returned from Brussels with his EU deal, the debate on the European Union has shifted significantly. The Remain campaign's case seems almost wholly based on what they describe as the nightmare of leaving. This case has in whole or in part become characterised by spin, smears and threats.

This was not what we were told the debate would be about and so for those keen to stay in the EU I register a concern and also a challenge.

In the last fortnight we have had a series of highly questionable dossiers – threatening almost biblical consequences if we dare to consider a future outside of the European Union.

We've seen a series of stunts, whereby big businesses, big banks, and powerful politicians from other EU member states seek to bully the British people into believing their jobs and security are at risk. The impartiality and integrity of the civil service – on whose credibility the whole institution of Government depends – has even been called into question by Parliament.

The acrimonious manner in which all this has been conducted is troubling, and will I fear have consequences long beyond June 23. After all, such desperate and unsubstantiated claims are now being made that they begin to damage the very integrity of those who make them in the eyes of the public.

The biggest danger to the European Union comes not from those who advocate departure, but from those who denounce such thinking as heretical and dangerous.

This is the most important question we have faced in a generation, and it is vitally important that the debate is conducted in a respectful manner – where we maturely interrogate the issues, rather than indulge in scaremongering.

And so that brings me to the challenge.

In January 2013, the Prime Minister made an excellent speech, setting out his vision for a reformed European Union. He made a powerful case for 'fundamental, far-reaching change' – without which he said the EU 'would make our countries weaker not stronger'.

Now, I know that the Prime Minister entered the negotiations with good intent. He said at the time that 'with courage and conviction, I believe we can deliver a more flexible, adaptable and open European Union'.

The problem was that he was faced with the final reality that the EU is disinclined to make such fundamental reform.

Now there will be some people who will have believed from day one that we should stay in the Union regardless, and others who may have wanted to leave irrespective of any changes that might have been secured.

However, the original referendum challenge set by the Prime Minister was not predicated on whether we wanted to remain in the EU or not – it was whether we wanted to remain in a 'reformed EU'. That is a vital distinction and one which is now being deliberately avoided.

After all, the Prime Minister said himself that the case for staying in was conditional on achieving reform. So for those who are undecided, surely the paramount question that they will want to answer for themselves is whether the European Union that we now have is reformed or not.

If they arrive at the conclusion that it has not, then it would be quite logical for them to decide that Britain would be better served Out.

The Secretary of State for Work and Pensions warned of lasting damage to British politics beyond the June 23 referendum if PM David Cameron (pictured) does not conduct the EU debate in a more 'respectful manner'

Perhaps that's why the terms of the debate seem to have been shifted by the Remain camp. They no longer seek to pretend the Prime Minister's deal amounts to fundamental reform.

Instead, the question being asked seems to be whether we could cope on our own at all. Why they would seek to present our country, and themselves, as so weak is beyond me.

But ask yourself this: with razor wire fences going up in mainland Europe due to fears of unsustainable levels of migration, with the failing euro creating economic misery for Europe's poorest people, with high unemployment and economic stagnation, is this a set up you would seek to join?

If the answer is no, then we as a country should have the confidence that, as the fifth largest economy in the world, we can have a more prosperous and more positive future if we take control of our own destiny.

We should not be intimidated into forgoing that choice.

Indeed, as the Prime Minister himself said in that same 2013 Bloomberg speech: 'Of course Britain could make her own way in the world, outside the EU, if we chose to do so.'