When Britain last held the presidency of the European Union, in 1998, the EU's foreign policy was in its infancy and its defence plans had not yet been drawn up.
The picture is very different today. This British presidency will have to grapple with a broad range of foreign initiatives, from negotiations over Iran's nuclear programme to helping to resolve civil war in Aceh, Indonesia, to aid in Sudan.
Britain will also seek to ensure the scheduled start of EU membership talks with Turkey on October 3, and to step up aid for Africa.
Since EU foreign policy is subject to national vetoes, such activity depends wholly on co-operation among EU member states. The most important relationship is between Britain and France. The two countries have driven the Union's security and defence policy ever since Tony Blair, the UK prime minister, and Jacques Chirac, the French president - eager to bury the memory of European inactivity during the crisis in the Balkans - sealed a defence deal at St Malo, France, in December 1998.
So far, Britain and France have managed to insulate this co-operation - intended to relieve pressure on each country's peacekeeping efforts - from tensions elsewhere, such as the 2003 war in Iraq, which divided them.
"The fact that Chirac and Blair were throwing jam rolls at each other at the most recent summit should not slow the process down," says Charles Grant, director of the Centre for European Reform, a London-based think-tank.
In the short term, the challenge is Iran, which insists its nuclear ambitions are peaceful but is suspected by the US and the EU of seeking nuclear weapons capability. In negotiations with Tehran, the EU has promised to come up with a new proposal by late July or August.
Unless that effort, spearheaded by the UK, France and Germany, proves successful, Iran is likely to resume parts of its nuclear programme, frozen until now.
That could prove a stiff test for the EU, which has promised Washington that in such circumstances it will help the US to refer the issue to the United Nations Security Council - even though France and Germany are among the biggest investors in Iran.
Before then, the British presidency will be working on contingency plans put forward by Maarti Ahtisaari, the former Finnish president, to send about 200 observers to oversee a possible peace deal for the 30-year-old civil war on the Indonesian island of Aceh.
The British presidency will also try to put finishing touches to EU-Nato co-ordination over support for an African Union observation mission in Darfur.
It will attempt to nudge the EU towards providing more aid for Iraq and establishing greater continuity between emergency help for Africa and longer-term support.
The UK also wants to keep the talks on Turkey on track, despite an apparent backlash against EU enlargement, and to maintain pressure for change in the western Balkans, such as police reform in Bosnia.
