The single market was almost a no-brainer, but we have achieved that, albeit with institutions designed for half the number of states that now make up the EU. But before rushing into further institutional reform the challenge first is to re-articulate the purpose of the EU. For me it is best conceived as a global EU, shaping the world of the 21st century - not by force, but by argument. It is not inconceivable that Britain could seek to take a lead in areas like climate change, global security and fair trade by ourselves, but it makes so much more sense to do it as a leading member of the EU.

Security is always the most fundamental role for government. The 9/11 attack was only the most grotesque demonstration of how this now more than ever means global security. And failed states are the most likely places where weapons of mass destruction could be developed beyond government control. EU military intervention has shown itself far more effective from the Balkans through DR Congo than the US approach in Iraq and Afghanistan. So continuing to participate in EU defence developments makes a lot of sense; this in no way means ceding national control, or scaling down NATO cooperation.

Skills alongside security are now more than ever a core responsibility of government. Without skills it is difficult for individuals or nations to participate effectively in the 21st century world. Anybody in business knows that so-called 'soft' people skills are at least as important as 'hard' technical skills. European experience can greatly strengthen these. Already the Erasmus programme has provided international learning opportunities for many university students, but those benefits should now be much more widely spread.

Sharing European experience offers particular opportunities in the public sector, where here in Britain centralisation over the last 30 years has produced a 'one best way' culture that has eliminated diversity, while innovation to improve services depends on opportunities to experiment with different approaches - the main reason for bringing in private and voluntary partners. EU partners offer a huge range of alternative tried and tested approaches ripe for investigation by people with a front line understanding of how things currently work, and where the problems are. Clearly the contexts will be very different, which is why it is not a case of simply copying, but of understanding alternatives.

Beyond skills it seems to me you cannot separate social Europe and global Europe. The WTO's Doha development round may yet stall, but if it does not the next round must be a 'social round' for issues like rights to union representation and workplace health and safety. A development round is primarily for low income countries to say what they need, alongside a certain amount of negotiating on other issues. But a social round needs someone else to take the lead and that someone should be the EU. As with other aspects of fair trade, this will benefit everyone who participates.

Not so much in Britain so far, but elsewhere for sure, there are questions over the geographical limits of the EU. It seems to me that the best way to ensure an outward looking global Europe is through establishing four firm outward-looking 'corners'. Already in the west Britain and Ireland will always feel a natural affinity not least of language and law with North America, similar to those between Spain and Portugal and Latin America. In the east Turkey and Ukraine should play the same role. Not least because Istanbul was the capital of the last Muslim empire, and Kyiv was the birthplace of medieval Russian Orthodoxy, they will always have strong ties to the Islamic world and Russia respectively. Which is not to say membership should be rushed. They are large countries with their own traditions. And it is their traditions and their links that will add most to the EU; in terms of population, given the current size of the EU, their significance is far less. Within these corners there is some room for flexibility, but these are the natural limits of any European Union, and should be recognised as such.

So much for positives - there are negatives. I don't think anybody in the mainstream of British politics will ever wholeheartedly support the EU until the Common Agricultural Policy is abolished, or substantially reformed. It just sends all the wrong signals. Britain has shielded itself from it with the rebate, but that could only ever be a temporary solution. The CAP is still the major block to the Doha WTO round, although that is not currently such a big popular issue, it is important for the Labour Party, because it is the foundation for people to trade themselves out of absolute poverty. But it also presents a huge opportunity for the EU to demonstrate its value on the global stage. To spend such a huge proportion of the EU budget on what is such a small part of the economy just sends all the wrong signals. I think it is unlikely, but not inconceivable, that the CAP could be the rock that breaks British support for the EU. I really hope it is not. British people will wholeheartedly support an EU perceived as a Europe for global security, soft skills and fair trade, rather than a Europe for supporting farmers.

Perhaps once these issues are resolved, in however many decades that will take, it will be time to return to the issue of an EU constitution, but for now it is an institution whose time has not yet come. But climate change, skills, security and trade present very real opportunities, for which further reform is needed, albeit reforms that 'only' need a new treaty.