The rescuers: From the bucket to the rice bowl - how the aid flows

A pound is thrown into a bucket. The money goes to a charity, which charters a plane. The plane is loaded with medicine, food and water and flown to Indonesia. The cargo is driven to someone who is sick, hungry and thirsty.

A pound is thrown into a bucket. The money goes to a charity, which charters a plane. The plane is loaded with medicine, food and water and flown to Indonesia. The cargo is driven to someone who is sick, hungry and thirsty.

A simple story. One that is not always true of charitable donations, which can be diluted by the costs involved in distribution. But in the case of the staggering millions given to the tsunami aid appeal in the last fortnight the overheads have been kept to a minimum. And the money trail can be followed in its simplicity from British pockets to disaster zones in Thailand, Sri Lanka and Indonesia.

Eight days ago, the villagers of Hawkinge in Kent were roused by knocking at their doors. On the step were Brendan-James or "BJ" Smith, seven, and his five-year-old twin brothers Spencer and Harrison, who were collecting anything their neighbours could spare for the boys and girls left homeless, orphaned and destitute by the tsunami.

The buckets filled. Over two days, trudging from door to door in the driving rain, the brothers raised £435. "The boys just said: 'Can't we do something to help?'" said their mother, Alison Smith. Yesterday they were at it again.

The money will follow an extremely efficient financial path from the buckets through Save the Children fundraising teams and the banks to hurriedly hired cargo planes and on to the Indian Ocean.

Over this weekend and the next few days, Save the Children, Oxfam and the Government are flying hundreds of tons of new aid to two of the most desperately affected areas: Aceh in Sumatra and the east coast of Sri Lanka.

Save the Children has two cargo planes flying out to Aceh this week. The first, a DC8 hired at a cost of $185,000 (£99,000), leaves from East Midlands airport carrying 30 tons of aid on Monday. Its contents tell their own story: tarpaulins for 15,000 families; rubber ground sheets; generators; large storage tents; 500 mosquito nets; 1.5 tons of children's clothing; and three tons of children's food supplements. The cost of this flight is being met by a private donor.

On Tuesday a huge Russian Antonov cargo plane will carry 10 heavy duty trucks and all-terrain vehicles for distributing aid. The Government has promised to meet the cost of many aid flights and the charity is hoping it will do so in this case. Save the Children is already in Aceh, alongside Oxfam and many other agencies, delivering food and essential survival kits.

Last Thursday, Oxfam flew out 53,000 litres of bottled water donated by the Somerfield supermarket chain, on board cargo planes donated by Sir Richard Branson's Virgin Atlantic Airways, for the Maldives where 30,000 people are without clean water.

British charities are also buying thousands of tons of food, medical supplies, clothing and tents from within Asia. The British Red Cross, which has received £5.5m so far, has sent seven planeloads of tarpaulins and kitchen supplies, worth £1m, from Pakistan and northern India to Sri Lanka.

Aid agencies are used to sudden but short-lived surges of public generosity. The response to the tsunami has been different: very many more spontaneous acts of generosity like that of the Smith brothers, coupled with a sustained level of commitment.

Unofficial estimates show the public has donated more than £122m to the tsunami relief. That figure is likely to rise by at least £12m in repaid taxes once the Treasury's Gift Aid scheme kicks in, and by millions more once the cheques are cashed.

Donations have run at an average of £10m a day for two weeks, and money is still arriving. Save the Children anticipates two very large private donations that could lift its own total from £1m to £1.5m this week.

The peak in donations came 10 days ago, on Thursday 30 December - the day the Smith boys decided to go door to door. This followed television appeals by David Dimbleby and Trevor McDonald and warnings from the World Health Organisation that the disaster had made five million people destitute.

Paul Cullen, Oxfam's head of supporter relations, calculates that its cash total is nearing £7.5m - including £2m which came in from collecting tins in shops. Oxfam normally has 12 people on its phones; at the appeal's peak it had 30 and had hired a call centre to handle the overspill. In the three days following the disaster, they took 7,000 calls at an average of £100 a time. At Save the Children's offices in London, staff took 11,000 calls in the middle of that week.

The scale of the public reaction has exposed one link of the chain to greater scrutiny than normal - the fees taken by banks and credit card companies to process donations.

Normally, credit card companies can trim off 1 to 3 per cent as a fee for each transaction - a charge that reportedly brought in £300,000 before the companies agreed, under intense pressure, to waive their charges.

The charities are trying to get the same deal from money transfer companies such as Western Union and MoneyGram, which are being used heavily to send money home to stricken relatives by Sri Lankans, Indonesians and Indians living abroad. Those negotiations, however, are proving more difficult.

Faced with embarrassing questions about the amount of money that could be trimmed off from donations, the Disasters Emergency Committee (DEC), the powerful co-ordinating body for the UK's 12 largest aid charities, has come down hard.

In the past, as much as 6p in the pound was taken off by charities for office costs and expenses. But the DEC announced late last week "to dispel any doubts", that it was imposing a strict ceiling on the administration fees allowed. Fundraising costs were limited to an "absolute maximum" of 2 per cent, with another 1 per cent going towards official monitoring and evaluation of how the money was spent. It added: "On average, 98p out of every pound goes straight on emergency relief aid."

The charities relish passing on the anecdotes about pensioners arriving in shops to hand over that week's pension; of one man who dropped £5,000 in cash on an Oxfam counter and just walked out; of queues forming as people wrote out cheques.

Then there was the man who was just about to book his summer holiday and decided to hand Oxfam £300 instead, or the elderly callers apologising profusely because they could only afford £10.

Over the Christmas holidays, says Mr Cullen, Oxfam staff were bringing their aunts, grandparents and children in to stuff envelopes and take calls when they would have been picking over the turkey, playing with presents and bickering over the television.

Christmas was, the charities believe, a crucial factor in the scale of the public response. Families were together at home, watching TV and with plenty of leisure time. The disaster also struck a region many Britons knew directly - such as the beach resorts of Phuket, Sri Lanka and the Maldives. And, because of the large number of Western holidaymakers with camcorders, they were able to see graphic, minute-by-minute footage of the unfolding disaster.

That, the aid agencies say, is very different from their experience trying to raise money for crises in more isolated but equally needy countries, such as Congo, Afghanistan and Darfur, Sudan.

The greater understanding for the areas affected is heightened by the scale of what happened.

Mona Laczo, 31, a veteran emergency worker overseeing Oxfam's 25-strong aid team in Aceh, said it was the worst-affected area she had encountered, after seven years coping with war and flooding in Afghanistan, Bangladesh and India. As she spoke to The Independent on Sunday, her building was shaken by yet another earth tremor.

"The devastation we see here is beyond description," she said. But the water buckets, latrines and trucks paid for when countless people shook tins or collected anything they could, such as the Smith brothers, were already transforming lives.

"In the first few days it was very, very evident that people were in shock, traumatised," she said. "But now people are at least smiling ... They've heard about the outpouring of donations and support from around the world. It does make them feel good, especially in Aceh. This whole area has been closed off. Now, they are on the map."