The UK government had secretly planned to train and equip tens of thousands of rebels to fight against Syrian President Bashar al-Assad, but the move was aborted, it has been claimed.
The idea was put forth by Lord David Richards, who was the then Chief of Defence Staff, and it was actively considered by David Cameron and the National Security Council.
According to the BBC's Newsnight programme, the initiative to train up to 100,000 anti-Assad forces, was under consideration two years ago, but was ultimately shelved because it was thought too risky.
Lord Richards had warned the Cameron administration that there were only two ways to resolve the Syrian conflict: either defeat Assad or let him win.
Under the plan, air cover was to be provided by the Western powers and Gulf allies so that the rebel army could press ahead against Assad in a "shock and awe" strategy similar to that of Iraq in 2003.
Top US officials, including General Martin Dempsey, Washington's top-most military officer, were also consulted on the matter.
The UK government has not responded to the disclosure.
Syria has been undergoing intense turmoil for the past three years as the anti-regime groups are relentlessly fighting to uproot Assad, but with little success. The crisis has claimed the lives of tens of thousands of people and forced millions to flee the country as refugees.
Syrian National Coalition spokesperson Monzer Akbik was quoted as saying: "The international community did not intervene to prevent those crimes and at the same time did not actively support the moderate elements on the ground."
"A huge opportunity was missed and that opportunity could have saved tens of thousands of lives actually and could have saved also a huge humanitarian catastrophe."
The Syrian civil war has also paved the way for the emergence of extremist Islamist groups such as the Islamic State of Iraq and the Levant (Isis) which is now marching ahead in Iraq capturing several key regions and establishing a hard-line Islamic caliphate.