Former Prime Minister Gordon Brown has warned the world not to put up new barriers to trade.
Giving evidence to the Commons International Development Select Committee he said that the fundamental restructuring of the world economy now going on could have enormous potential for Africa, but only if rich countries did not return to protectionism.
Apart from a brief late-night intervention in a debate on a constituency matter, this was the first time Mr Brown had spoken at Westminster since losing the election in May. He asked to give evidence to the committee in their investigation of Britain's aid budget - a topic important to him.
Mr Brown said that economies in sub-Saharan Africa had grown strongly in recent years, and had recovered more quickly from the global financial meltdown two years ago than economies in the developed world.
But protectionism could harm that progress, and he appealed to the world to continue to pursue a shared vision to cope with the challenges ahead, saying that "the biggest danger is protectionism of the mind".
He said that in 1933, at the London Economic Conference, the world had failed to see that free trade would be the best way out of recession, turning instead to "a decade that turned into protectionism and war".
He said that he had taken this message to the US Congress, but did not get great applause.
He reeled off a blizzard of figures about Africa - 40 per cent of the population have mobile phones, three million have been saved through immunisation. But paying the $180 (£135) per year to put every child in Africa through school was not an "ambitious target", rather it was a "moral demand" on the world.
But he said that investors had ignored the potential of Africa. "After the dotcom bubble the private sector should have moved to the area of unexploited opportunity which is Africa infrastructure investment, instead moved into sub-prime mortgages."
Like his predecessor Tony Blair, whose first Commons appearance after he left office was also in front of this committee, Mr Brown clearly sees African development as an issue he can focus on now out of power.
He spoke movingly about the numbers still dying from disease and poor maternal care, speaking of countries where childbirth can be a death sentence, so that "mothers go to say goodbye to their friends before the impending birth of a baby because they think the chance of surviving that childbirth are very limited".
He warned that "this could be a lost decade for growth" in Africa, if trade barriers go up and aid pledges by rich countries are not fulfilled. He was asked if Italy's failure to honour its aid promises would damage Africa.
He said he would not criticise any single country, but the target of 2015 to hit the Millennium Development Goals would not be achieved if countries did not pay what they had agreed for aid.
He defended his government's record in doubling the proportion of GDP spent on aid from 0.25% to 0.56%. The coalition government that succeeded him have committed to continuing the increase until it reaches the target figure of 0.7% in 2013. Mr Brown said that it was important to monitor whether this was achieved by sustained increases to the development budget and not just a one-off payment to the World Bank in 2013.
Mr Brown also warned of the challenges of China's rise. He said that this was a battle for influence in Africa. He said that China did not see aid in the same way as western nations. They were now the sixth largest donor to Africa, but the system still had to show that it could meet the challenges of this new economic power.