There is a certain irony to launching the UK’s first World Trade Week at a time when activity is contracting faster than at any time since the global economy was shut down by the second world war. Even so, it makes the event all the more relevant because trade is not just an indicator of the health of the business world – it is a determinant of it.

So far, with some exceptions, the general guard against protectionism adopted by the G20 leaders seems to be working. I suspect that there are a number of reasons for this. The first is our supply chains, which are so integrated that protectionism simply isn’t as easy as it used to be. The second is the fact that everyone is watching everyone else. There is a lot to be said for international peer pressure under these circumstances.

But most important is the World Trade Organisation (WTO) system itself, which has proved to be an extremely strong legal check on protectionism. At a time when we are focused on the flaws or failings of international governance, it is important to recognise that we have built a system in the WTO that works and must be protected.

However, this is no argument for complacency. Maintaining the integrity and openness of the WTO system means constant vigilance. To reflect this, the UK government is to co-finance an independent watchdog. Global Trade Alert will unite a worldwide network of think tanks to provide governments with independent analysis of trade-distorting policies. It will produce evidence of the damage protectionist policies are doing and advise on the least protectionist ways to provide support and stability to economies through the downturn. This will run alongside the monitoring that the WTO and other bodies are already doing on behalf of the G20.

This needs to be backed by further practical measures to keep trade flowing – both here in the UK and worldwide.

It is hard not to put the Doha Round at the top of this list. The Doha Development Agenda would be a huge stimulus package – perhaps producing €120 billion in gains to the global economy. It would benefit developing countries in particular, most of which cannot afford fiscal stimulus packages of their own. It would lock tariffs at around their current levels, providing insurance against future protectionism.

None of this will be possible unless we can rebuild a consensus on the value of free trade. Even before this crisis, popular support for globalisation, free trade and open markets was vulnerable – especially in the developed world. The rise of China and the massive scale of global financial flows created a sense that globalisation was eroding our control over our own lives, serving the interests of the global rich, sidelining those of the global poor.

There is no point in defenders of open trade pretending there is nothing at all to these arguments. There is. That is why we now recognise the need for global governance of financial markets and financial flows. It is why the Doha Round demanded far more of developed countries than developing ones. It is why open markets have to come with policies to help people live with the rapid economic change they bring.

But open trade didn’t cause the credit crunch. It didn’t cause the recession. Open trade remains the single most important way we know of expanding economic opportunity and lifting people and societies out of poverty. It will be the key to a sustained and global recovery from the recession.

It was Keynes who said the mistake free traders often make is to defend their case solely on the cheapness of traded goods. Of course people want cheap goods. But trade is also about open societies and about opportunity: the moment when a small business in Europe realises there is a market for what they make in China or Brazil, or vice versa. The case for open trade has to be built on the opportunities that come from trade and on the value of open societies over closed ones.

It is now 70 years since the first national World Trade Week was launched in the US during the Depression. Those 70 years have seen tumbling trade barriers for industrial goods and the creation of a rules-based global trading system.

That trading system faces a huge crisis of demand and credit but the real long-term risk to its health lies in protectionism taking on a new veneer of respectability in the current economic crisis. Open trade needs defenders now more than ever.

I believe preserving that openness is one of the key benchmarks by which we will judge political leadership in this crisis. In World Trade Week I think that’s a benchmark well worth aiming for.

Lord Mandelson is first secretary of state and business, innovation and skills secretary

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