The reported comments by MI6 chief Sir John Sawyers that Iran would likely achieve nuclear weapons by 2014 only confirm what was indisputable to anyone who has looked at the evidence. Iran wants nuclear weapons and is fast developing the capacity to construct them. This is not based on shady intelligence or dodgy dossiers. The evidence of Iran's nuclear weapons programme was scrutinised for years by the IAEA - a cautious multilateral body not given to alarmism - before they declared it 'credible' in a detailed report published in November 2011.

This was nearly ten years after Iran's secret and illegal uranium enrichment facility at Netanz, and heavy water reactor at Arak were first uncovered in 2002. These facilities were not necessary for its legitimate civilian nuclear programme, but were important for developing the fuel for nuclear weapons. It was this discovery that set the IAEA inspectors on the trail of Iran's true intentions. Iran's failure to disclose the Natanz and Arak facilities were only the most blatant of many Non-Proliferation Treaty breaches, leading the IAEA to declare Iran 'non-compliant' with its commitments in 2005.

Tehran has since ignored a string of binding UN Security Council resolutions demanding Iran cease its illegal activities, and only increased the scale of its programme, and enriched at levels every closer to weapons grade uranium. Iran was caught lying again in 2009, when another secret enrichment facility - not big enough to make civilian fuel, but just big enough for weapons fuel - was discovered at Fordow.

In the last few months Iran rejected new demands from the IAEA to inspect the Parchin facility where they believe Iran has been testing explosives for a nuclear trigger, and the Iranians have been covering up what it was doing there. If all that were not enough, David Cameron warned a Commons committee in March that Iran is developing missiles that would potentially provide a delivery system for nuclear warheads to reach as far as London.

Should Iran succeed to develop these weapons, it would shift the regional balance of power in its favour. Iran has a violent anti-Western regional agenda which includes support for extremists throughout the region, including those fighting British forces in Afghanistan, armed Palestinian radicals opposed to peace, and the Assad regime in Syria. Iran also has a strategic goal to attain hegemony over the Gulf, which is the source of a significant percentage of the world's oil, threatening global oil markets and the UK economy. Acquisition of nuclear weapons will enhance Iran's capacity to promote its dangerous agenda, enabling it to threaten its smaller, pro-Western Arab neighbours and, with its long range missiles, Europe directly. This would likely lead to a Middle East arms race, as Arab states would seek to obtain weapons to deter Tehran.

How to stop Iran getting the bomb, including whether or not to use force, provides sharp policy dilemmas, but no one should be in any doubt about the cost of failing to do so.

This piece was co-authored by Jules Robinson

Toby Greene Agrees