Failure to monitor the effectiveness of how Britain's foreign aid is spent risks undermining public trust, according to Christian Aid.

A report from the National Audit Office (NAO) into the UK's overseas aid spending identifies weaknesses in how the £12 billion spending is monitored, because instead of all being spent through the Department for International Development it is spread across 14 different departments.

At around 80 per cent, DfID is still the largest spender by far and was praised by the NAO for improving its monitoring.

However, Sir Amyas Morse, head of the NAO, said: 'The Government has decided that departments and cross-government funds other than DFID should have responsibility for expenditure which makes up the 0.7 per cent aid target.

'This means that meeting the target has become a more complex undertaking and the resulting gaps in accountability and responsibility require more effort to manage.'

Christian Aid's Head of Advocacy, Laura Taylor, said the report 'shows that the Department for International Development is a world-leader when it comes to the transparency and efficiency of aid spending and has been very focused on ensuring that UK Aid works as hard as possible to improve the lives of the poorest and most vulnerable'.

However, she said: 'The government's strategy, to increase to 30 per cent by 2020 the amount of UK aid managed by departments other than DFID, is clearly risky. Today's report reveals that these departments are less experienced and less transparent in using aid money.

'There is a danger that public trust is undermined by a government policy that does not hold all aid spending to the same set of standards.

'Therefore increases to other government departments such as the Foreign Office should be frozen until they can prove they meet the same high standards in terms of quality and transparency as DFID.

'This should give them time to focus on the quality of their aid spending before the quantity they are asked to spend increases too significantly, and will help to ensure that aid is spent on what matters most – improving the lives of the poorest people in the world.'