One of the most unanticipated lessons I learnt from my 10 years as British Prime Minister, was not about the power of government but its limitations. There are, of course, things that only government can do and reforms only government can enable. The profile of government, however, as the sole means of effecting change and therefore the vehicle into which all efforts for change should be put, is misleading and wrong.

When first elected you think: you have got the top job; you know what you want to do; you set it out campaigning for office; surely, once you have the top job, the decisions will be made, the action will follow. My first term was a learning experience in the difference between intention and delivery, between saying and doing. The perception may be the absolute power of the top person; the reality is one in which you are regularly blocked by politics, by bureaucracy, by the innate tendency to inertia of a system designed to manage the world not change it.

In my second term, I created systems to break the blockage: government working together with the private and philanthropic sectors to implement change. And in terms of reform the second five years were much more radical in many ways than the first.

Part of the difference lay in appreciating the extraordinary and dynamic role of the Philanthropic sector. Today's 11th Global Philanthropy Forum registers an opportunity to see how far this sector has developed and how much more it could develop further.

Some philanthropic institutions are global names today such as the Gates Foundation and Clinton Global Initiative. This in itself is new, and proof of their impact. Others are less well known but no less effective. Their reach is now felt in obvious spheres like health, education and poverty relief. But increasingly, this 'third sector' is supporting initiatives in business development, women's empowerment, human rights and the improvement of government itself. There are traditional parts of the sector such as the Faith community, which, for example, provides almost half of all health care in Africa. But there are also sprouting up scores of small start-up philanthropic institutions that will operate at a niche level, but make an extraordinary difference with very ordinary amounts of resource.

In the USA, the philanthropic sector is most advanced. At roughly $290 billion per year it is several times the size of the US Aid budget. 11 new foundations and over 100 non-profits are created every day. Even in the UK the amount given is bigger than many departmental budgets; and in Asia and the Middle East there is a huge growth in the sector which though still way behind the US, now runs into billions of dollars every year.

The work these philanthropic institutions do is crucial precisely because of the limits of government. They can't and shouldn't substitute for things only government can do. But that still leaves a pretty big range of activity and though only government or legislatures can pass laws, one huge lesson we're learning from governments around the world is that the private and philanthropic sectors or partnerships between them and government, are often more efficient ways to get government programmes done.

This is because the best philanthropy is not just about giving money but giving leadership. The best philanthropists are those who bring the talents that made them successful into their charitable work. Those talents - determination, drive, refusal to accept the conventional ways of doing things - are just what some of the world's problems need.

Philanthropy can be creative. It can act quickly. It can spot opportunities that governments are slow to spot. To take just one example, Bill Clinton's initiative noticed the fact that drug prices for HIV-AIDS would stay high unless countries could buy in bulk. They provided guarantees on drug purchases and as a result costs plummeted, saving lives across the globe. And, in a great example of how government and philanthropy complementing each other, this scheme and President Bush's radical efforts to tackle HIV-AIDs through the PEPFAR programme fitted closely together -multiplying their impact. Above all, philanthropy can go across the boundaries of Government and nation. It can do this not just in how it acts but how it thinks.

So when I left traditional politics in 2007, I decided to build foundations that could be catalytic in nature in tackling the problems I could see as Prime Minister but which I knew the normal processes of government would not confront, at least in the right way.

One was the Tony Blair Faith Foundation, which creates programmes of education and action around the idea that people of different religious faiths have to live with each other and learn from each other if we are to combat extremism and have peace in today's world. The era of globalisation is pushing people together. Different cultures have to co-habit in ways that earlier generations never had to. The risk for the 21st century is not fundamental conflicts of political ideology. It could easily be conflicts of cultural ideology. Culture is often defined by faith. But faith can divide as well as inspire. It's an issue that has to be addressed. My purpose is to show why and how.

The Africa Governance Initiative is a non-profit dedicated to improving governance in Africa. The idea here is that yes aid is vital and has brought real benefits; but actually Africa's destiny lies in the hands of Africa's new generation of decision-makers. The real inhibition on growth and prosperity today is not aid from the outside; but good governance on the inside and that means not just honest government but effective government. So we put teams of people who have hands on experience of delivering government programmes alongside the Presidents of countries who have the right vision but lack the levers of delivery. We work there; live there; and transfer those skills in basic programmes like child mortality, infrastructure, and attracting inward investment.

I also have a Sports Foundation in the north of England, because for me sport should be part of mainstream policy, open to everyone, not an optional extra.

But the point from my own situation is a more general one. Philanthropy is so exciting because it allows people to bring their different experiences - as business leaders, thought leaders, or political leaders and apply them in new ways, to new problems. This is absolutely the right moment for government to do all it can to promote philanthropy; and certainly nothing to harm it.

I have found working outside of the well-worn trammels of Government rewarding, inspiring and, potentially, with more influence than my time in politics. It is that reflection that makes today's event and celebration of philanthropy so important.