Britain's biggest foodbank charity has defended its latest figures claiming more than one million people used food banks in the last 12 months.

According to latest figures released by the Trussell Trust this week, foodbank use rose to more than one million with four in 10 of those needing help being children.

The trust, which is Britain's biggest foodbank charity, said there were more than 1,000,000 claims for at least three days' emergency food from its foodbanks in the last 12 months, more than in any previous year.

After the independent fact checking organisation Full Fact challenged the claims on its website, Trussell Trust issued a clarification.

The trust said: "Trussell Trust figures show that Trussell Trust foodbank use has hit one million for the first time, but we have not claimed that the numbers relate to unique individuals.

"The Trussell Trust is measuring volume – the number of people to whom it has given three days' food. The Trussell Trust has consistently measured figures in this way and reports them at the middle and end of each financial year.

"Trussell Trust figures clearly state that we are counting the number of people to whom we have given three days' food – these are not necessarily unique people. Year-on-year, the figures are showing an increase in numbers given three days' food by Trussell Trust foodbanks.

"As our press release says, 49 per cent of people coming to Trussell Trust foodbanks in a year needed help once. On average people needed two foodbank vouchers in a year. Each foodbank voucher entitles people to three days' food and support."

The trust also emphasised its figures relate to Trussell Trust foodbanks and not to the hundreds of other independent food aid providers. "There is no official data on other food aid projects, but some people estimate that there are likely to be the same number again of non-Trussell Trust foodbank style projects in the UK."

The trust added: "Our focus remains on the people behind these numbers, and the fact that more people than ever have been referred to Trussell Trust foodbanks for three days' emergency food is deeply concerning."

Full Fact said the claim that more than a million people are using Trussell Trust food banks was inaccurate and came from confusing the number of different people using Trussell Trust food banks in a year with the number of times they use the food banks.

"The Trussell Trust say that on average people needed two food bank vouchers annually, so the number of people using food banks is likely to be around half of the 1.1 million figure."

The service is "emergency food and support", not sustained food provision. About half of users needed one food bank voucher in a year, though a significant minority, about 15 per cent, used the service more than three times.

Full Fact also noted that supply is not the same as demand.

"The rise in uses of Trussell Trust food banks came with a rise in the number of food banks themselves, up from 56 food banks in 2009 to 445 food banks in 2014. "This represents a major expansion of the Trust into new areas." The trust served 29 UK local authorities in 2009 but that number increased to 251 by 2013.

"The increase in supply doesn't necessarily reflect an increased demand for emergency food. There may have been people in need of emergency food in the past who wouldn't have shown up in the Trust's figures because there was no Trussell Trust food bank nearby," said Full Fact.

Academics from Manchester University have said that while a social stigma remains in using food banks, there is an increasing "normalisation" in their use due to the growth in the number of food banks and food donation points in supermarkets.

Full Fact admits there may be around 800 food banks across the UK. There are also other providers of emergency food assistance such as soup kitchens and Meals on Wheels, adding up to about 1,500 emergency food assistance providers in Britain.

The coalition government rejected the link between benefit reforms and food bank use.

But an analysis in the British Medical Journal found the increase in use and number of food banks was associated with spending cuts, benefit sanctions and unemployment.

Full Fact concluded: "Data from the Trussell Trust may be the best evidence we have, but reporting on the subject needs to be clearer about the limitations of the evidence to inform debate about such a serious issue."