UK policy in Syria has been hampered by "wishful thinking", says a former top military adviser in the Middle East.
Lt Gen Sir Simon Mayall said the UK had underestimated the staying power of President Bashar al-Assad.
In an interview with BBC Newsnight, he painted a picture of a UK being in a strategic muddle over Syria and described Russia's intervention as "hugely significant".
Lt Gen Mayall spent much of his career in the Arab world - including as deputy commanding general of coalition forces in Iraq 2006-2007, and Defence Senior Adviser Middle East 2011-2015.
It has emerged recently that during discussions in 2012 of possible plans to hit Syrian President Bashar al-Assad's forces, General David Richards, now Lord Richards, chief of the general staff asked rhetorically whether the prime minister was sure Britain was about to bomb the right people.
Lt Gen Mayall says he argued at that time, "that the Assad regime would fight to the last", but that policy makers had got caught up in the excitement of the Arab spring and hoped the Syrian leader would be swiftly overthrown.
The Russians, he believes were, "in many ways more realistic about the staying power of Assad".
Russian President Vladimir Putin has argued in recent weeks that his country's operation in Syria is designed to prevent the type of state implosion that took place in Libya after Nato's intervention there in 2011.Video Title: Russia intensifies air strikes in Syria for third day. Source: CCTV America. Date Published: Oct 2 2015.
The British general's remarks show there is some sympathy for this objective among senior officers in the West, particularly after Western experiences there, in Iraq following the 2003 invasion, and in Afghanistan.