UK foreign policy on the Syrian crisis has been branded "appalling" and "naive to the point of being totally unrealistic" by the director of one of Scotland's leading international aid charities.
Alistair Dutton, of the Scottish Catholic International Aid Fund (Sciaf), said British interventions in the region have served to strengthen opposition forces and prolong the conflict, now approaching its six-year anniversary.
He called on UK ministers to accept that the best option for stability in the country is for Syrian President Bashar al-Assad to regain control.
Mr Dutton made the remarks during a visit to Lebanon to see how cash raised by Sciaf is helping the 1.5 million Syrian refugees who have fled there since 2011.
His comments come as Syrian government forces, backed by Russian allies, have taken nearly all remaining rebel-held parts of Aleppo amid reports of civilian killings.
Mr Dutton said: "British foreign policy is appalling towards Syria.
"It is naive to the point of being totally unrealistic and everybody I speak to in the region says we have got it wrong, and we are only making the situation worse and prolonging the civil war."
Mr Dutton added that senior figures from the region have said "the best solution for Syria is to build a future which allows for Assad to be the Syrian leader".
He stressed: "I'm not an apologist for Assad. What is happening in Aleppo is unforgivable.
"I'm as disgusted as anyone by the dreadful atrocities he has committed both in Aleppo and elsewhere.
"There is little doubt that he will continue to act in the most vicious and violent way in his quest to reassert control over the country.
"But no matter how immoral and inhumane his actions, holding to the current absolutist stance on Assad will only prolong the war and the unimaginable suffering of the Syrian people.
"His inhumanity should be contained by human-rights monitors, backed up by UN peacekeepers, which should be part of any settlement, not by the hopeless insistence that he is removed."
The UK Government has provided "non-lethal" equipment and political support to moderate Syrian opposition groups in the region, while in 2013 MPs rejected proposed air strikes in response to Assad's suspected use of chemical weapons.
Mr Dutton said such intervention was a "pure ego trip for people who say something must be done and some politicians need to sit on their egos and not do something if it is going to make it worse".
The Sciaf director, who has 20 years' experience in the humanitarian aid and international development sector, said he supported the Government's policy on refugee resettlement, taking people from camps in places such as Lebanon to the UK, but added its target of 20,000 was far too low.
He said "the principle that we will decide what (number) we can look after, we will come to where you are and on the basis of need we will determine who those people will be" was "sensible".
Mr Dutton further hit out at UK arms sales to Saudi Arabia amid its involvement in the Yemen civil war.
Sciaf has launched an appeal to help provide food, water and shelter to those affected by the conflict.
"The British Government must stop supplying military equipment and technical support to the Saudi regime while it brutally commits war crimes and human-rights abuses on the civilian Houthi population," Mr Dutton said.
On Syria, a Foreign Office spokesman said: "Assad continues to refuse to let the UN deliver supplies to the hundreds of thousands of people he is besieging.
"Even if Assad re-imposes his rule over Aleppo, millions of Syrians will remain unwilling to accept the dominance of a tyrant who has the blood of hundreds of thousands on his hands.
"The only real solution for peace and stability in Syria is an enduring political solution based on transition away from the Assad regime to a government representative of all Syrians."
Referring to Saudi Arabia, the spokesman added: "We take our arms export responsibilities very seriously and operate one of the most robust arms export control regimes in the world.
"The key test for our continued arms exports to Saudi Arabia is whether there is a clear risk that those weapons might be used in a serious violation of international humanitarian law. The situation is kept under careful and continual review."