The international community must establish "humanitarian corridors" between Syria and neighbouring countries to prop up a hospital system that has lost thousands of doctors and is "rapidly" running out of life-saving supplies, one of Britain's leading surgeons has said.

Vascular surgeon David Nott, who last week returned from a six-week trip to northern Syria, said that doctors and other healthcare workers were being targeted by the regime, and that aid supplies were being disrupted by Islamist militants who were increasingly at war with both the Assad government and the rebel Free Syrian Army.

Mr Nott, a seasoned emergency medic who has worked in conflict zones including Bosnia, Afghanistan and Iraq, worked 18-hour days at a field hospital in a rebel-held area, one kilometre from the front line, during an aid mission with the charity Syria Relief.

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Operating with Syrian surgeons under shellfire and with minimal equipment, Mr Nott said the hospital was seeing more than a dozen gunshot victims a day – usually civilians targeted by regime snipers.

"There aren't many doctors now in that part of the country, and only a handful who are surgically trained. The ones that are left are those that really want to help the people," he said. "That's why the majority of people are dying – the surgeons are not trained in trauma, in how to deal with massive bleeding."

"The hospital I operated at didn't have a hat or a mask for a surgeon to wear. So much stuff is needed there because it all runs out so rapidly. To get the supplies across the lines is the big problem. There needs to be some kind of humanitarian corridor set up, either by the UN or even the British government. We need a humanitarian channel so that the aid can come in."

His call comes amid growing frustration among aid organisations at the international community's failure to address the humanitarian crisis facing Syria. While the arrival of UN weapons inspectors tasked with destroying President Assad's chemical weapons ended a diplomatic impasse between Western nations, who back the rebels, and Assad's ally Russia, it has done little to help the millions of civilians caught in the conflict.

"This population needs external assistance … The UN Security Council [agreement] hasn't changed anything," said Dr Jean Hervé Bradol, research director at Médecins Sans Frontières, who returned from Syria two weeks ago. "The agreement they made wasn't followed by any concrete consequence to the civilian population … Nothing has changed. It's very striking that the international community is pleased with the chemical agreement yet nothing significant has changed … Realistically, we would like to be in a position to send convoys into the area where the most vulnerable population is under attack, yet at the moment this looks like a dream."

Last week, six volunteers from the International Committee of the Red Cross and one volunteer from the Syrian Arab Red Crescent (Sarc) were kidnapped by armed men near the town of Saraqeb in Idlib province. Three of the ICRC volunteers and the Sarc volunteer have been released but, despite repeated appeals, their colleagues are still being held. The incident has again highlighted the dangers faced by aid workers in Syria.

Entering the country from Turkey, Mr Nott had to hide in the back of his vehicle at checkpoints manned by fighters from the Islamic State of Iraq and Syria (Isis). "The problem is that the aid is being stopped by Isis," he said. "It's very difficult to get in or out. If they don't like you they will pull you out and arrest you and kidnap you."

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He said that healthcare workers and medical facilities had become targets for regime forces. "If you take out the health workers, nobody wants to fight because there's nobody there to put them back together again," he said.

"One hospital we passed has been levelled to the ground. Our hospital has been targeted by Scud missiles. They are trying to blow up all the hospitals. We had drivers coming back with bullet holes in their ambulances. The regime has spies around, and if they know who the doctors are they will find out who their relatives are and arrest them or detain them, or do something awful to them."

Syria Relief and Islamic Relief UK backed Mr Nott's call for humanitarian corridors. Martin Cottingham, from Islamic Relief UK, said: "We've been pressing for humanitarian corridors for some time now.

"Since the start of the conflict, 15,000 doctors have left Syria and in some areas there is just one doctor per 70,000 people. Hunger is also a real issue. As winter approaches, the need for these humanitarian corridors for aid to get to remote areas is essential." He added that a humanitarian corridor would need to be set up by "a coalition of the willing, a combination of government and the UN". France called for humanitarian corridors last year but the plan failed amid fears it would need enforcing militarily.

Mr Nott, who returned to work in London last week, said that he was grateful to have had the opportunity to teach local surgeons techniques such as clamping blood vessels and sewing up holes in the heart, which can save the lives of bullet-wound patients, most of whom had, before his visit, been bleeding to death.

"I've never performed so many thoracotomies [chest openings] in my life because there were so many people being shot in the chest," he said. "People were bleeding to death because nobody had taught the surgeons how to open the chest up to control the bleeding from either lungs or heart or the major blood vessels."

"With me there teaching them, it was a different matter, but I wondered how they were going to get on after I left. I was so happy to receive an email from them [last week] to say they had done exactly what I'd taught them – and that more patients were surviving."

Food for Syria

The United Nations estimates that four million Syrians are now in need of emergency food. Save the Children's chief executive, Justin Forsyth, adds that "with winter looming and hunger needs set to grow... we need humanitarian access to all communities in Syria in weeks, not months". Currently, only organisations that have been approved by the government, such as the Syrian Arab Red Crescent (Sarc), can distribute aid within Syria. "But deliveries of food rations continue to be delayed due to security risks on the roads, checkpoints... and the constant shift of control lines across the country," says Abeer Etefa, a spokesperson for the World Food Programme (WFP). Entering from open border crossings – such as Al Arida, Al Masnaa, Abboudiyeh on the Lebanese border, and Lattakia Port, in north-western Syria – supplies have to pass through checkpoints controlled by opposing forces, while "drivers get stopped, hijacked and sometimes the cargo gets looted or worse", according to Simon Hacker of the WFP.

Could humanitarian corridors work? They would require Syrian approval or an international mandate. The MP Brooks Newmark argues that "the initiative has to come from within the regime itself; it has to allow safe passage to the various relief agencies working in Syria and take responsibility for protecting its civilians". Attempting to set up a corridor without the regime's approval would be dangerous. "No country would put its soldiers at risk in that way," he says. "The Russians have a moral obligation to put pressure on the regime to let humanitarian aid get to innocent civilians."

Chris Doyle, director of the Council for Arab-British Understanding, says: "Corridors... need to be protected, yet nobody is prepared to supply troops, or has thought about where these corridors would go, and... no space is safe. All fighting parties need to agree on free access to humanitarian agencies and to avoid, at all costs, the politicisation of aid."

Lord Ashdown agrees on the problem of safety: "A humanitarian corridor is a very good idea, but who is going to protect it?

Amy Lewin