David Cameron sprang to the defence of Britain’s aid policy and under-fire MP Andrew Mitchell as he insisted sending money overseas was the “right thing” to do.

The Prime Minister defended the Government’s policy of protecting the aid budget while cuts are being made on spending at home in a major speech.

The comments were a boost for Birmingham MP Andrew Mitchell (Con Sutton Coldfield), the International Development Secretary, who has been attacked for insisting Britain’s aid spending should increase.

Mr Mitchell last week suggested the nation should be proud that Britain is an “aid superpower”, but he was criticised by some Conservative MPs who suggested that money should be pumped into the defence budget instead.

Speaking at the Global Alliance for Vaccines and Immunisation conference in London, also attended by Mr Mitchell and Microsoft billionaire Bill Gates, Mr Cameron admitted: “The way we are protecting our aid budget is controversial.”

But he added: “I think there is a strong moral case for keeping our promises to the world’s poorest and helping them even when we face challenges at home.”

And he told critics: “To those who say fine but we should put off seeing through those promises to another day because right now we can’t afford to help - I say we can’t afford to wait.

“Three children die every minute from Pneumonia alone. How many minutes do we wait?

“I don’t think 0.7 per cent of our Gross National Income is too high a price to pay for saving lives.”

The Government has pledged to raise the foreign aid budget to 0.7 per cent of gross national income, and enshrine the figure in law.

It would mean spending on international development rises from £7.5 billion last year to £11.4 billion in 2013, an increase of 34 per cent, after taking inflation into account.