Leading article: Some modest successes eclipsed by one big failure

When the Prime Minister addresses the Lord Mayor's banquet in the City of London this evening, he is expected to focus on the high principle of global interdependence in the 21st century and the hard necessity of reaching agreement on a new round of world trade talks at the Hong Kong summit in December. Equity in world trade is one of Mr Blair's favourite themes, and a worthy one. It is a cause in which he has shown admirable consistency and commitment. And it is a thoroughly praiseworthy topic to broach before a City audience.

But Mr Blair will also make clear that he views trade as one of many challenges that can only be met multilaterally and in a global context. Security and prosperity at home, he will reiterate, will not be achieved unless issues such as terrorism, trade, climate change and poverty are also addressed.

Which is why it is worth considering how Mr Blair, now into his third term at Downing Street, has fared in tackling the many other aspects of British foreign policy. This has been a highly privileged year for Britain in the international arena, and one for which Mr Blair harboured great ambitions. With both the chairmanship of the Group of Eight and, in the latter half of the year, the Presidency of the European Union, Britain has had a rare opportunity to set the international agenda and project its own priorities. Mr Blair also enjoyed another advantage: he is now among the world's longest-serving leaders and won a new domestic mandate in May.

Despite these assets, however, success has been distinctly mixed. On the plus side there has been the prominence Mr Blair and the Chancellor, Gordon Brown, gave to Africa at the G8 summit and the deal that was reached on African debt. But this was less than had been hoped for, and implementation is still in doubt. The military involvement in Sierra Leone remains a bright spot, but Britain has failed to make the slightest impact on Robert Mugabe's tyrannical mismanagement in Zimbabwe.

The balance in Afghanistan remains positive, but delicate, with Britain's particular responsibility - for curbing the opium trade - a dismal failure. A three-party European effort to solicit nuclear guarantees from Iran is in abeyance following the unexpected election of Mahmoud Ahmadinejad, but it need not yet be written off. In the Middle East, Britain has remained a peripheral player, its effort to hold a peace conference undermined by the absence of Israel. Relations with the United States are cordial, but - as Sir Christopher Meyer's memoirs confirm - they are far too much of a one-way street.

Europe is an especially bleak area. With the EU constitution rejected by France and the Netherlands, and Germany for much of the British presidency in the throes of an election, Mr Blair had an opportunity to make his mark. Instead, Europe has almost vanished off the foreign policy spectrum. Britain was wrong-footed over the start of talks on Turkey's accession and, on the budget, some real flexibility over the British rebate might have set a more propitious tone. An agreement in December would repair some of the damage, but there is no certainty at all that this will be attained.

The bleakest prospect by far, however, is Iraq. Neither interim elections nor the constitutional referendum have brought any diminution in the violence, which is spreading to the hitherto relatively peaceful south. And while the bitter diplomatic fall-out from Britain's military involvement may be declining in Europe, it remains a liability in the Arab world - and a continual drag on Mr Blair's credibility at home. Trade with the countries of Africa may illustrate the extent of global interdependence, but so too - in a more malign and more immediately dangerous way - does the invasion of Iraq.