A Strategic Defence Review is essential in the current situation of military commitments abroad at a time of economic downturn. Hard choices must be made for the present and the future. The question is whether this review will be able to rise above the lobbying of all the vested interests, and also whether a future Tory government would adhere to the recommendations.

We must also bear in mind that the scenario may change in the future. The last SDR, for example, looked at expeditionary warfare, but it could not forecast that we would be attempting nation-building as we tried to do in Iraq and we are now trying in Afghanistan.

The bottom line is that we cannot continue with the kind of commitment we have without increasing the defence budget. We need to make economies and choices. The argument of the Army – that we are fighting a landlocked war in Afghanistan, so why are we spending on aircraft carriers and fast jets – is a view I have some sympathy with. But the Afghan war will not last forever, just as the Northern Ireland conflict and the Cold War did not.

We are an island and a trading nation so we need to maintain our lines of supply, and for that we need a navy. I don't think we need these very expensive aircraft carriers; cheaper alternatives can be found. We can also ditch the Eurofighter which has become an unnecessary luxury. Significant savings can also be made by reforming the procurement system, which is a mess. We should look at buying much more equipment off the shelf.

But then we come on to the vested interests: the MPs with jobs to get for their constituencies and companies lobbying hard for manufacturing contracts. These are issues which need to be addressed.

The author is the former commander of the Royal Marines and is Visiting Professor of War Studies at King's College London