For Gordon Brown, foreign policy will pose some of his most difficult challenges – but also some important opportunities. Since 9/11, the main foreign policy focus has been security and counter-terrorism. The challenge for Brown will be how effectively he can combine a firm stance on security with a renewed emphasis on what Robin Cook described as the ‘ethical dimension’ of foreign policy.

Looking at the decade ahead there are some pretty tough challenges. First, climate change has already been identified as a clear policy priority with the publication of the Stern Report. Second, tackling the threat of terrorism will remain a priority both in domestic and foreign policy. Third, confronting global poverty and trade injustice, which are causes that Brown has championed in government. Fourth, the UK’s relationships with our EU partners and with the US are at a critical juncture. Fifth, can we strengthen multilateral institutions like the UN so that they are more effective and gain credibility? Sixth, can real progress be made in the Middle East?

Iraq has dominated foreign policy discussion for almost five years. One effect of this is to divert public attention from areas where the UK has played an important progressive role: including on the environment and global warming; promoting an arms control treaty; and seeking reform of the United Nations.

Whatever the short-term holds in Iraq, the long-term prognosis for the Middle East is pretty clear: a settlement of the Israel-Palestine conflict is a necessary but not a sufficient condition for regional peace and stability. The tough challenge is how best to promote change in the region – not least in Iran and Syria.

Tony Blair has sought to be a bridge between the US and the EU; this fundamental view of the UK’s role is highly unlikely to change. Brown may offer a change of tone, and will probably be more openly critical both of the US and of the EU in areas of disagreement like climate change, or Guantanamo in the US case, farm subsidies in both cases, and economic reform in the EU.

Of course, it is not only the UK which faces a forthcoming change in political leadership. France will have a new president this year and the US elects a new president next year. There is real potential for serious shifts in policy in both these crucial countries after Jacques Chirac and George W Bush leave the stage.

Brown has already provided a flavour of his approach to foreign policy with his recent Guardian article emphasising the importance of support for primary education in Africa and restating the priority he attaches to tackling climate change. His final budget as chancellor and the comprehensive spending review will provide opportunities to put further flesh on the bones of these key areas, as well as setting out the resources and reforms necessary to promote security and defeat terrorism.

Blair made climate change and Africa the two priorities of the UK’s presidency of the G8 in 2005, but progress was often overshadowed by Iraq. A change of prime minister will be a point at which these two critical issues can be emphasised, particularly if the budget and spending review show the way.

Finally, let me suggest three specific areas for action in Brown’s first 100 days. First, he should immediately sign the UK up to the European Convention Against Trafficking, a straightforward and clear symbol of the importance of the ethical dimension. Second, a determined push for real action to protect the people of Darfur, demonstrating that the cause of progressive interventionism remains alive and relevant. Third, use the opportunity of Chirac’s departure to forge a new approach in Europe which makes the pro-European case on bread-and-butter issues like energy and climate change, rather than on Grand Designs and institutional changes.

Internationalism is a core principle for Labour. As chancellor of the exchequer, Brown has combined substance on the economy with a passion for social justice – foreign policy will give Prime Minister Brown the chance to combine substance on security issues with a passion for global justice.