I agree with David Cameron. Yesterday he told the UN General Assembly that “when we make a promise to the poorest people in the world, we should keep it, not turn our back on people who are trusting us to help them.” But I really wish that he would keen the promise that he made in his manifesto and legislate for the commitment he reaffirmed yesterday. On page 117 of the Conservative manifesto, his commitment, and the timing of it, was explicit:

“Will be fully committed to achieving, by 2013, the UN target of spending 0.7% of national income as aid. We will stick to the rules laid down by the OECD about what spending counts as aid. We will legislate in the first session of a new Parliament to lock in this level of spending for every year from 2013.”

This was reaffirmed in on page 22 of the coalition agreement:

“We will honour our commitment to spend 0.7% of GNI on overseas aid from 2013, and enshrine this commitment in law.”

Just after the new Development Secretary Justine Greening was appointed, the Chancellor argued that “it is not about legislation; it is about delivering the money." But I beg to differ.

Yesterday, UK development NGOs were falling over themselves to welcome the Prime Minister’s declaration at the UN but the NGOs are at risk of being outmanoeuvred on this issue.

No doubt the aid budget in 2013/14 will represent 0.7 per cent but DFID will almost certainly underspend it. This is because the budget has effectively been frozen since 2010 and so will jump by a third in 2013. Greening will be under pressure to deliver another underspend in 2014/15 after which the future of the aid budget will be subject to the next round of election manifestos.

I predict that, as opposition from their backbenchers grow, the Conservatives will commit to an independent review after the next election, much like the one on tuition fees after the last election and like the review on the third Heathrow runway after the next election. The UN’s 0.7 per cent target is 40 years old, after all.

Labour and the Liberal Democrats will be under no electoral pressure to create a political dividing line on this issue. In fact the opinion polling suggest the opposite. Their political incentive will be to wait for the outcome of such a review to neutralise the debate until after the election.

I have written for New Statesman about the importance of the promised legislation many times before (here, here, here and here). But after the reshuffle, I am now more convinced than ever before that if the NGOs can’t secure the legislation in this Parliament, and thus require another vote to repeal it, then the UK’s aid budget will only remain at 0.7 per cent for two years.

Justine Greening may be the first Development Secretary in British history who didn’t want the job. Metro newspaper claimed she said “I didn’t bloody well come into politics to distribute money to people in poor countries” [as in the print version, although now removed from online as Greening's office disputes the quote], while The Times said three No 10 sources claimed said she argued for an hour at Downing Street on reshuffle day.

When Greening is reported as saying she wants the aid budget to “do more, with less” I feel conflicted (Greening denies having said this). I like the first sentiment but not the second. Everyone wants taxpayers money spent well and if after two years of operation, Andrew Mitchell’s Independent Commission for Aid Impact isn’t working, then Greening is right to be focused on value for money. But the government did inherit a department that the OECD and the ONE campaign consistently ranked as a global leader in aid effectiveness.

On Newsnight last night, David Grossman rehearsed all the arguments about why the aid budget should not rise as promised. But the most compelling argument of the night was put by Adrian Lovett of the ONE campaign: that you can’t clear the deficit by cutting the aid budget anyway. Recent IPPR analysis of the big choices facing politicians in the next Spending Review shows that the planned rise in the DfID budget is just a rounding error in the public finances. The big choices are about the NHS budget, the welfare budget, future tax rises and crucially, the pace at which the deficit is reduced. Even if you scrapped DfID entirely, you’d still have to face up to one of these four big public spending choices.

The spirit of Make Poverty History is needed now more than ever. IPPR and the ODI have studied UK public attitudes towards international aid and development as a contribution to the next phase of UK campaigning on poverty reduction and global development. It is time for NGOs to stop apologising for politicians and campaign for them keep their promises. If the promised legislation is not secured in the next two years, the NGOs will only have themselves to blame.

UPDATE 26/09/2012 16:00

A DfID spokesperson said:

"Justine Greening's views are clear. She has said "Delivering on our promise of 0.7% is the right thing to do, whether it's helping countries cope with natural disasters and famines, or working with some of the British charities who are world leaders in international development. I will critically assess our budget on behalf of the British taxpayer to make sure that, pound for pound, it goes exactly where it's intended and where it can make the biggest difference."

Richard Darlington was Special Adviser at DFID 2008-2010 and is now Head of News at IPPR - follow him on twitter: @RDarlo