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

When the Prime Minister recently said that ISIS represented the greatest threat in a generation to our security he was right. Although I believe Russia is, arguably, the biggest single state-on-state threat that the NATO alliance faces, the inexorable rise of Islamist fundamentalism, manifested currently by ISIS and other groups in the region, has both regional and global ramifications. The migrant exodus towards Europe and the destabilisation of Turkey’s borders are only two of the ways in which violent jihad in the region threatens to spill out and contaminate a much wider area.

There are a number of steps that we can and should take. The first is to increase the number of UK air strikes as a proportion of the coalition total. Ministers are fond of saying that the UK is second only to the United States in the number of strikes undertaken but the hard numbers show that US forces have carried out around 92 per cent of the strikes, the UK 4 per cent and all the others put together another 4 per cent. There is no point in having defence forces if they are not deployed against what the Prime Minister describes as a threat of this level.

The next thing to do is to get our Arab coalition partners to pull their weight. It is, after all, their region and they cannot expect the West to constantly intervene to deal with problems that are, at least partly, of their own making.

By the same token, greater consistency and political engagement by the Obama White House in the region would not go amiss.

The next change to make is to alter our absurd policy of hitting ISIS in Iraqi territory but not in Syrian territory. In reality, the border is non-existent but if ISIS forces are aware that they can act with impunity in one area, supplying and strengthening forces in another, then they will do so. Parliament (mistakenly in my view) voted against the use of airstrikes against the Assad regime when it used chemical weapons against its own population, and in doing so strengthened the view of the jihadists that the West was in retreat and increasingly isolationist, but it has never said that we should not use our airpower to attack the savagery of ISIS, not least against those poor souls who live within their territorial control.

Again, where there are other regional ISIS strongholds, such as in Libya, we should regard them as legitimate targets. Where we should stop and pause for breath, however, is in the deployment of British ground forces (as has been suggested recently, for example, by the former chief of the defence staff General Sir David Richards). It is certainly true, as military chiefs repeatedly point out, that you cannot win a military conflict from the air alone – history is littered with examples of this particular lesson. What we should remember, however, is that we have offered to give air support in the campaign against ISIS to our Arab allies so that they could more effectively combat them on the ground.

Before any British government commits troops to a ground war there are four questions that need to be answered. First, what does a good outcome look like? Second, can such an outcome be engineered? Third, do we need to be part of such engineering and fourth, how much of the aftermath do we want to own?

One of the reasons why I was in favour of punishing the Assad regime for the use of chemical weapons but not becoming embroiled in the Syrian civil war was because I believe it is very difficult to answer even the first of those questions. As I described in my book, Rising Tides, Syria, like Iraq, is an artificial, post-World War I construct. There is an internal tribal power struggle and a secular versus religious struggle. On top of this there is a proxy battle between Saudi Arabia and Iran centred there and power rivalry between United States and Russia. Aggravating all of this is the increasingly bitter intra-Islamic struggle between Sunni and Shia Moslems. Just what a “good outcome” looks like against this complex historic backdrop is extremely difficult to say. The Prime Minister is quite right to resist the deployment of British troops until the strategic picture becomes much clearer. The lives of our armed forces men and women are too precious to be put at risk without clear objectives and a credible exit plan.