David Cameron has renewed his pledge to spare foreign aid from future Conservative spending cuts, arguing that recession-hit voters would understand the UK's "responsibility" to the world's poorest.

The Tory leader said if the party won power it would impose tougher controls to ensure development money was not mis-spent and to show taxpayers where every penny was going.

Mr Cameron stressed that the temptation to switch the money to meet domestic needs would be a "serious long-term mistake" as it would help foster terrorism, climate change and war, posing security risks at home.

The Conservatives are committed to meeting a United Nations target for countries to increase aid spending to 0.7% of GDP by 2013, making it one of only two areas, with the NHS, protected from future spending cuts.

According to the party's new strategy, more aid money would be made dependent upon results and more would be put in the hands of communities and individuals. Spending would be overseen by an independent watchdog.

Launching the proposals at the London headquarters of Save the Children, Mr Cameron told activists Britain was "not a country of fair-weather philanthropists".

He went on: "I understand why people might say that at a time like this, in economic circumstances like these, that increasing the amount we spend on foreign aid is the last thing we should do.

"But economic difficulties at home should be the time for us to re-affirm our moral responsibilities, not reduce them."

Mr Cameron said he wanted ministers to be able to point to individual items - such as malaria nets - that British taxpayers' cash had bought in a bid to ensure public support.

The public would be given a say on what issues a "whole chunk" of the foreign aid budget would be spent on and more of it would be channelled through aid agencies, he said.

The UK Government has imposed a 10% cap on the amount of aid money used to tackle climate change.Douglas Alexander, the International Development Secretary, accused the Tories of failing to make a similar promise. "They have refused to give a clear commitment to how they would deliver resources to tackle climate change and its effects. This casts doubt on their commitment to honour Labour's aid promises," he said.

Phil Bloomer of Oxfam welcomed Mr Cameron's commitment, saying it was a sign of progress that all of the UK's three main parties were now signed up to a "moral duty they cannot ignore".