It wasn't just the NHS budget that the Cameroons pledged to ringfence and protect in opposition, as part of their failed "detoxification" and rebranding of the Conservative Party between 2005 and 2010. The aid budget, we were told, would be protected too - Bono  appeared via video link at the Tories' annual conference in 2009 to heap praise on Cameron and co for signing up to the 0.7 per cent pledge .
But let's be honest: the aid budget isn't an issue that tends to be at the top of politicians' or journalists' priority lists. It can be so easily overlooked, forgotten and/or ignored.
So yesterday, in a speech at the London School of Economics, Labour's deputy leader, Harriet Harman, who is also the Shadow Secretary of State for International Development, was right to flag up the "fragile" nature of the Conservatives' pledge on international aid and the need for a Labour-led grassroots campaign to keep up pressure on the coalition to deliver for the developing world:
With the Tory Party commitment to the 0.7 per cent being fragile , with the opposition from within their own ranks so virulent, with growing public anger about the effect of the cuts on domestic priorities, alongside a strong public belief that "charity begins at home", no-one should take it for granted that the Tories will inevitably deliver on their pledge. The fact that the two parties of the coalition government and the official opposition all agree on this target should not lull anyone into a false sense of security that its achievement is a foregone conclusion.
So, we cannot simply wait for the pledge to be honoured, we must remake our arguments for it. It is time for "a Keep the 0.7per cent / 2013 promise" campaign. We are launching it next week. I am sure that we can look to young people, the churches, the aid agencies and our diaspora communities to support such a campaign - as they did so much to campaign for the original promise and so strongly backed the actions our government took to increase aid and drop debt.
She went on to make this rather important if depressing observation:
Despite the government's commitment to UK aid reaching 0.7per cent of GNI by 2013, the Spending Review Statement of last October froze the aid budget as a percentage of GNI for the next 2 years.
The cost of this 2 year freeze - instead of continuing the upward trend we established - is £2.2 billion which would otherwise have been available in development aid.
...Abandoning the steady progress towards the 2013 target, instead of building on the progress that was made when we were in government will require a big jump in the aid budget in 2 years time. Following the 2 year aid freeze, to meet their promised target by 2013, they will need to boost the aid budget by 31% in a single year - an increase of approximately £3billion - in 2013.
Does anyone - apart from perhaps Steve Hilton - really believe that's going to happen in the run-up to 2013?