At the Chilcot inquiry into the Iraq War, Tony Blair claimed the risk of terrorists being supplied Weapons of Mass Destruction by “rogue” states justified a policy of invasion rather than containment and deterrence. Alex Holland analyses this argument for regime change.

Unlike Blair’s more reasoned cases for military intervention on humanitarian grounds in countries like Kosovo and Sierra Leone, his argument to the Chilcot inquiry about Iraq was less robust.

Liberating Iraqis from Saddam's brutal rule had become the most popular defence by pro-war apologists after WMDs were not found in Iraq. Chilcot asked the former Prime Minister if Iraq was about regime change. “No, the absolutely key issue was the WMD issue,” said Blair.

Furthermore, Blair repeatedly stressed to the inquiry that it was his fear of 9/11-style attackers using WMDs that changed the “calculus of risk” away from containment and in favour of invading Iraq.

This may seem a compelling argument to people who have watched television series such as 24. In such fictional portrayals, murky rogue states hand over briefcases containing nuclear bombs to suicide bombers ready to detonate in downtown LA.

In reality the number of cases of biological and chemical attacks by extremist groups has been tiny and nuclear attacks non-existent. This is because most often conventional weapons are better at achieving the extremists' aim of killing lots of people.

Indeed the sarin poison gas used in the 1995 Tokyo Underground attack by the religious group Aum Shinrikyo is a case in point. The gas itself only killed 12 people while costing millions of dollars to produce.

Professor David C Rapoport, a long-standing expert on terrorism, has noted: “The plain fact is neither chemical nor biological weapons presently are truly weapons of mass destruction in the way atomic weapons are; and they are certainly not so in the hands of terrorists.”

There are doubtless willing martyrs who have dreamed of using a nuclear weapon to send themselves and others to oblivion. However those foreign governments who might not weep to see mushroom clouds over the UK are unlikely to rapidly hand over such weapons to fanatics.

There are many reasons for this. One is the cost of developing atomic bombs for a poorer country. A successful nuclear programme represents an enormous investment in terms of money, skill and resources.

AK47s or rocket propelled grenades, on the other hand, can be dished out relatively freely to non-state groups. Giving ruinously expensive atomic weapons away to a shadowy outfit so they can launch an anonymous attack on behalf of your regime is much less likely.

Why would it have to be an anonymous attack? Because if a “rogue” state openly threatened a country like Britain, Israel or the US with a nuclear strike, that regime would run the risk of its country being turned into radioactive ash. These established nuclear countries could and would launch a devastating counter-attack with their own much greater nuclear arsenals.

Trying to keep involvement in a human-delivered WMD attack secret by minimising a government’s role, such as by not sending handlers with a bomb, runs its own high risks. The less connection a state has that could link them to a group, the less control they have over how a weapon might be used. The extremists might attack somewhere other than Washington or London. They might decide a city in their own region or country was a more deserving target. They could even use it on those who have given them the weapon.

Regimes that have supported extremist militants have often seen these militants come back to attack them in return. One example of this, shown in Jason Burke’s superb book, Al Qaeda, is how Pakistan and the US both eventually suffered at the hands of Islamic fighters they had supported in the Afghan-Soviet war.

Then there is the question of who WMDs would be given to and why. With Iraq there was no evidence connecting Osama bin Laden’s network to Saddam Hussein. Shia Iran is not a country that generally gets on well with fundamentalist Sunni bombers who view them as heretics.

Given all the problems of supplying Al Qaeda-style groups with atomic bombs, new entrants to the nuclear club are far more likely to hang on to them for the same reasons the UK seems to – for national prestige and to defend against bullying or attack by another nuclear power.

It would be better if no one in the world had WMDs at all, as President Barack Obama advocates. But for governments that insist on having them, as Iran might in the future, containment and deterrence almost always cost less to our safety than invasion and occupation.

This is especially so when you consider the radicalising effect the invasion of countries like Iraq has on communities that home-grown bombers have come from. These domestic attackers have been the greatest threat of this type to our security so far.

Moreover, since an invasion destroys the security apparatus of a state, that state’s ability to guard any WMDs it might have is eroded. This would increase the chances of WMDs being stolen by groups that otherwise wouldn’t have obtained them.

That terrorists may someday get WMDs is within the realms of possibility. But when analysing the “calculus of risk” such a threat poses to British lives and security, it does not outweigh that of invading and occupying other countries, which brings the certainty of radicalising elements at home and abroad.

Containment and deterrence of countries like Iraq may not be cheap or clean as Blair pointed out at the inquiry. But compared with the catastrophic costs of the Iraq invasion, it was the better option then and it is the better option with Iran now.

Alex Holland is a reporter on defence and security issues, and is Associate Editor of The Samosa. He is also a Labour Party council candidate for Brixton Hill, Lambeth, in South London.