Media playback is unsupported on your device Media caption Up to 250,000 spinning flowers were installed as a visual petition at Hyde Park as part of the If campaign to end world hunger

The UK has committed to giving an extra £375m to help feed the world's poorest children.

The aid is part of a £2.7bn global agreement aimed at preventing millions of infant deaths.

Prime Minister David Cameron led a high-level summit where delegates committed to supporting a historic reduction in "under-nutrition."

Organisers of a rally in London said 45,000 people turned out calling for global leaders to end world hunger.

Meanwhile, UK church leaders have called on the G8 to tackle tax avoidance by firms working in developing countries.

Austerity concerns

As part of its G8 presidency, the event in central London aimed to get more funding from nations, companies and charities toward African countries' own nutrition plans.

Media playback is unsupported on your device Media caption David Cameron: "We'll never beat hunger just by spending more money"

The UK committed an additional £375m of core funding. The Department for International Development added that if other donors raised £560m, it would would match this at a rate of 2-1, which would see an extra £280m paid from 2013 to 2020.

Mr Cameron backed a target of saving 20 million children from chronic malnutrition.

Under-nutrition is a chronic lack of nutrients that can result in death, stunted growth and in a lower resistance to illnesses in later life.

It is the biggest underlying cause of death in under fives in the world, responsible for 8,000 child deaths each day.

International Development Secretary Justine Greening said under-nutrition was stopping children and countries from reaching their full potential, accounting for the loss of billions of dollars in productivity.

Analysis This meeting may highlight a potential difficulty in involving the private sector in charitable work. At least three of the companies attending the summit make use of numerous tax havens - which aid agencies, and the Prime Minister himself, have spoken against. The charity Action Aid, has published data showing that Unilever, Glaxo Smith Kline and Vodafone - all of which have extensive operations in the developing world - also have subsidiaries in numerous tax havens. Action Aid campaigns for countries to pay more tax in developing countries. The charity stressed that the use of tax havens did not in itself prove tax avoidance, but did highlight the extent to which multinational companies operate in places that provide tax advantages. The three named companies all told the BBC they pay the taxes due in the countries in which they operate. Vodafone said the Action Aid research was flawed and misleading. The Prime Minister has said countering tax avoidance is a priority during this year's British Presidency of the G8 rich-country grouping.

"A strong and healthy workforce is vital if a country's economy is to prosper," she said.

"The commitments secured today will help transform the life chances of millions of children and pregnant women by ensuring they get the right nutrition at the right time, securing greater long-term economic growth and prosperity for all."

Mr Cameron acknowledged concerns as the country goes through a period of austerity, but said international aid was equivalent to "just over 1p" from every £1 of tax collected from the British taxpayer.

He insisted that Britain was "out in front" in reaching the target to give 0.7% of GDP because its people are concerned with trying to help those who are suffering in other countries.

"We accept the moral case for keeping our promises to the world's poorest even when we face challenges at home," he said.

"When people are dying, we don't believe in finding excuses. We believe in trying to do something about it."

Earlier he highlighted the public's generous response to appeals to disasters abroad.

"In short - it says something about the kind of people we are. And that makes me proud to be British," he said.

'Tax havens'

Meanwhile, the leaders of the Church of England and the Roman Catholic Church in England and Wales have joined international charities in a campaign called "If...", warning that displacement of small farmers from their land, unfair terms of trade and tax avoidance all contribute to hunger among the poor.

Speakers at the Big If London rally included the Microsoft founder Bill Gates, the former Archbishop of Canterbury Rowan Williams - who led a minute's silence - the Homeland actor David Harewood, film director Danny Boyle and a video message from David Beckham.

A colourful visual petition, made up of 250,000 spinning flowers, was also installed in Hyde Park, the charity Save the Children saying their petals represented the millions of children who die because of malnutrition each year.

In a video message, The Archbishop of Canterbury Justin Welby urged campaigners to keep up the pressure on world leaders to tackle global hunger.

He told activists: "We've come to celebrate the opportunity we have to end hunger in our lifetimes.

"The only way that's going to happen is by mass movements of people, like yourselves, getting together."

Charity Action Aid published data last month showing that at least three of the companies attending the meeting with the prime minister, all of which have extensive operations in the developing world - Unilever, GlaxoSmithKline and Vodafone - have subsidiaries in numerous tax havens.

Action Aid campaigns for companies to pay more tax in developing countries.

Media playback is unsupported on your device Media caption Microsoft founder Bill Gates: "We need to be more generous"

The charity stressed that the use of tax havens did not in itself prove tax avoidance, but did highlight the extent to which multinational companies operated in places that provide tax advantages.

The three named companies all told the BBC they paid the taxes due in the countries in which they operate. Vodafone said the Action Aid research was flawed and misleading.

Mr Cameron has said countering tax avoidance is a priority during this year's British presidency of the G8 group of leading industrialised nations.

World hunger is expected to be a prominent issue when G8 leaders gather between 17-18 June in Lough Erne, County Fermanagh, Northern Ireland.