As Syrian society teeters on the edge of final collapse after three years of ferocious warfare and economic devastation, the UN is making its biggest-ever appeal for £4bn in aid to help the country’s starving civilians.

Three-quarters of Syria’s 22.4 million people will need humanitarian aid to survive by 2014, according to a UN study. Bread in some areas costs five times what it was at the start of the conflict, and 80 per cent of Syrians say their greatest fear is shortage of food.

The former Foreign Secretary, David Miliband, who is now chief executive of the relief charity International Rescue, warned that the refugee crisis in Syria is “the biggest humanitarian test of the century” – a test that the international community is failing. The relief effort is being crippled by a lack of funds from donors and increasing danger for relief workers, he said.

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Snow is worsening conditions for the 2.4 million Syrian refugees who have fled to Lebanon, Jordan, Turkey, Iraq and elsewhere, while another four million people have been displaced within Syria.

Doctors are trying to stop a polio epidemic with an emergency immunisation campaign. Whole districts have been rendered uninhabitable by the government bombardment that inevitably follows a rebel takeover in urban and rural districts. Many people inside and outside Syria are reaching the end of their savings after three years in which a lot have been without a job. The violence is still getting worse, sending more people fleeing for safety elsewhere. On Sunday, government air raids, using explosives packed into barrels, killed at least 76 people, including 28 children, according to the Syrian Observatory for Human Rights. Relief workers said that as many as 50 more people might be trapped under the rubble but they did not have heavy equipment to rescue them.

Meanwhile, the Observatory said that 28 people from the Syrian minorities – in this case believed to be Alawi and Druze – had been killed by rebels in the town of Adra north-west of Damascus.

As the Syrian conflict enters its third year, many parts of the country are besieged and cut off from supplies of food, electric power and water. The UN sent a plane on Sunday from Arbil in Iraqi Kurdistan with food and other supplies for the winter to the Kurds of Hassakeh in north-east Syria – where fighters from among the 2.5 million Syrian Kurd population have been battling against al-Qa’ida-linked affiliates seeking to get possession of the oil wells in the north-east of the country. The flights will bring in 400 tonnes of food and 196kg of medical equipment. There is great variation in the degree of impoverishment, with people in state-controlled areas much better off because they are able to get bread at very low prices from government bakeries – though they often have to queue for a long time.

In central Damascus, Tartous and some other government-held areas it is possible to have a near-normal life. But food bought in the market, such as lamb, cheese, eggs and margarine, have all soared in price because they are not being produced or the roads are too difficult for food supplies to be easily or cheaply transported. Even where people have jobs, salaries have often fallen below £100 a month.

In rebel-held areas the situation is much worse. Food is in short supply and government salaries and pensions, however inadequate, are not being paid. A recent graduate from the University of Damascus, writing for IRIN, the UN news agency, said that there are few doctors in the besieged town of al-Hajar al-Aswad in south Damascus – and those that remain say that mothers are too undernourished to produce breast milk for babies and there is no powdered milk available.

One doctor said adults “are getting by on small amounts of seasonal stocked traditional Syrian foods like olives, thyme and marmalade – and in some cases cats and dogs”. He expected adults to start dying of starvation in the near future.