Media playback is unsupported on your device Media caption Bill Gates: 'There will be trade-offs'

Reducing the UK government's commitment to foreign aid spending would cost lives, American billionaire philanthropist Bill Gates has warned.

The Microsoft founder urged the UK to keep spending at least 0.7% of national income on foreign aid, saying it was proof of its goodwill and humanity.

Theresa May has refused to say if she will retain the spending pledge in the Conservative's election manifesto.

But the Scottish Tory leader pledged her own "absolute" commitment to it.

More than £12bn was spent in aid in 2015. Some newspapers and Conservative MPs argue the figure is too large and too wasteful, and some of it would be better spent on schools and hospitals in the UK.

Ruth Davidson told BBC Newsnight: "I think that international aid not only benefits… the countries that receive it but we benefit too.

"It takes moral courage to be one of the leading countries that espouses that, when there are a lot of countries that don't do it."

Culture Secretary Karen Bradley has also defended the commitment, saying she was "very proud" of the UK's track record in "helping the most in need".

At a speech in London, Mr Gates said Mrs May had made it clear during her visit to the US in January that she saw the 0.7% aid commitment as a "critical pillar" of Britain's foreign policy.

"Britain should be praised, not ridiculed, for sticking to this commitment," he told the Royal United Services Institute.

"It was a well-considered decision that sets an example for other wealthy Western countries. It also is visible proof of the UK's goodwill and humanity.

"Withdrawing aid would cost lives - which is reason enough to continue it," he added.

"But it would also create a leadership vacuum that others will fill, undermining the UK's influence in these regions."

'Hostile treatment'

There has been growing speculation that the Conservatives will attempt to row back on the aid commitment in their manifesto.

Newsnight political editor Nick Watt said there was pressure in Whitehall to subsume aid spending in a larger budget, which would include defence and trade, to give the government more flexibility in how the cash was spent.

Image caption Ruth Davidson said international aid benefited the UK too

The commitment to spend 0.7% of national income - or GDP - on foreign aid was enshrined in law with the backing of the Tory-Liberal Democrat coalition in 2015.

Former International Development Secretary Andrew Mitchell told Newsnight: "Around the world we are lauded and respected for the lives we are saving, but in Britain it receives very hostile treatment from elements of the press."

But former No 10 policy chief Camilla Cavendish said "many" people thought the commitment was too much, and pointed out that UK was the second biggest aid donor in the world.

Brexit backdrop

Mr Gates, who has conducted a round of interviews on the issue, told the Spectator that aid was "applied in places where the interventions are at least a hundred times more effective than anything you'd do domestically".

"If you can't save a life for less than 1,000 dollars, it's not done.

"Nor is it done unless there's a strategic goal - in terms of reducing pandemics, or creating stability to avoid war and migration.

"So you're getting something back, avoiding problems for the UK and in particular the US."

Mr Gates also questioned whether the UK was stepping away from its international commitments amid the backdrop of Brexit.

"Are you just getting away from the rule-setting on migration and tariffs, or is it a statement about stepping away from the entire world, and being generous to others?" he said.

In the past, the prime minister has praised Britain's aid spending as proof of its global leadership.

But in the Commons on Wednesday, Mrs May refused to confirm that her election manifesto would renew the commitment, saying only that the Conservatives were committed to "ensuring the defence and security of this country and to working for a stronger world".

A Conservative spokesman said: "This government takes its international responsibilities seriously and as a global, outward-looking country we will continue to support the poorest people around the world.

"As for our manifesto going in to the election, we will set out our plans in due course," he said.