Foodbank Australia says it is concerned about how it will source extra food to meet a possible increase in demand if changes to welfare go ahead.

Food bank charities in the United Kingdom have reported thousands more people turning to them for help since welfare reforms were introduced there in 2013.

Foodbank Australia says the welfare changes outlined in this week's federal budget could see a similar situation occur locally.

Gerry Andersen, the CEO of Foodbank New South Wales, says the organisation was already expecting to see an increase in demand in coming years.

"In the next three years our estimate is our demand will double.

"So we'll go from around about 5,000 tonnes in this financial year, which finishes at the end of June, in three years time to that being 10,000 tonnes."

However, he says there are now fears the welfare changes could see the increase in demand supersede what has been predicted.

Mr Andersen says families are already under pressure because of the "general toughness of the economy" and higher petrol prices.

"The thing that our survey showed was that it's the lower income families who are affected, these people are still working, but they just don't have quite enough money to go around," he said.

The budget has proposed a range of measures including cuts to family benefits which would save the Government $1.9 billion, changes to how young people access the dole, at a saving of $1.3 billion and $450 million of savings in changes to the pension.

It also includes plans to introduce a fuel excise and $7 GP co-payments.

The Trussell Trust, UK's largest food bank network, says it has seen a 163 per cent rise in the number of people accessing its services since the introduction of welfare reforms there in 2013.

It says more people are being referred to its services than ever before.

The Trussell Trust's chairman Chris Mould says half of the referrals to food banks in 2013/14 were as a result of benefit delays or changes.

"In the last year we've seen things get worse, rather than better, for many people on low incomes," he said.

"It's been extremely tough for a lot of people."

Welfare reforms in the UK have included sanctioning payments if certain conditions are not met, capping benefits and cutting social housing allowances if people have a spare room.

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Dennis Curran from Loaves and Fishes, another food bank charity in the UK, told the Scottish Parliament Welfare Reform Committee more people are struggling.

"We've got people with children and they are walking three and four miles to get to us," he said.

"We got a phone call just the other day from a social work department [saying] 'Can you give us food for a family that they don't need to cook because they have no money for their electricity'.

"We don’t need to have meetings to decide whether benefit cuts have got something to do with the rise in food banks. My seven-year-old grandson could tell you they have."

Mr Andersen from Foodbank New South Wales says a new warehouse is going to be built in the state, three times larger than the one currently being used, to meet rising demand.

All states in Australia, other than Tasmania, are already facing increases in demand.

Mr Andersen says low income earners are facing tough decisions.

"Food has become a discretionary spend because they still need to pay their electricity, they still need to put petrol in their car, to be able to get to work and all those things.

"Unfortunately it's put pressure on the children and the parents trying to feed those kids.

"We've got evidence that about 2 million Australians need our help every year, but half of those are kids and that's a pretty daunting task," he said.

With the possibility of an even greater demand for food, Mr Andersen says there are concerns about supplies.

"Our biggest concern is to be sure we can get enough of the right food.

"The model that Foodbank was founded on in 1992, which was 22 years ago, was that we would rescue food from the major manufacturers and retailers that might be a bit close to best before date or might have the wrong packaging or it might be a discontinued line or slightly damaged packaging," he said.

"But that model to a major degree has matured and Foodbank Australia gets some minimal funding from Kevin Andrews' department and we use that to source food from the manufacturers.

"Somebody will donate some wheat and somebody will convert that into flour, that flour is then converted into pasta or weet-bix or one of those types of products.

"But we're not getting anywhere near enough of the food, so that's one of our worries as to how we're going to be able to fund that future growth to have enough food available."

Dr John Falzon, CEO of the St Vincent de Paul Society National Council, is also concerned Australia could see a similar situation to that reported in the UK.

"People are being called upon to make absolutely impossible choices," he said.

"The choice between putting a meal on the table and being able to fund a child's school excursion the next day. Or a choice between paying the rent and paying the electricity bill so that you can heat your home in winter.

"These are not the kind of choices that people should be faced with in a rich and prosperous nation such as Australia."

He says the St Vincent de Paul Society is also expecting to see an increase demand for its services.