The charismatic and articulate Tony Blair, who entered Number 10 Downing Street on a wind of change as leader of what he and his colleagues dubbed the 'New Labour' and who saw Britain through a period of economic buoyancy, has left office somewhat sullied by the company he kept and a few dubious decisions during his 10-year leadership.

His unflinching support for United States President Bush's push for regime change in Iraq caused many of his parliamentary and party colleagues to withdraw their support. In effect, his forced early departure from office had little to do with failed domestic policies or major crises in his government. Rather, he was seen as being too willing an accomplice with the American president in trying to deceive the public about Iraq's having weapons of mass destruction, thereby providing Washington with the pretext for a war being pushed by neoconservative ideologues.

Still, Blair's appointment as a Middle East envoy to act on behalf of the United Nations, the European Union, the United States and Russia indicates that he remains a respected figure to significant sections of the international community. Mr. Blair will find it at best challenging fulfilling his new role as Mideast envoy. Quite apart from the notoriously difficult diplomatic minefield he will have to traverse, there is the question of whether some groups will find in him someone whom they can trust.

His successor as leader of Britain, Gordon Brown, will also be faced with his own challenges: that of trying to convince the public that he stands on the opposite side of the fence to Blair on key policy matters; and to act in a tangible way to demonstrate this difference.

While lacking Blair's telegenic appeal, Brown is sufficiently self-possessed to be able to stamp his own imprimatur on British and world politics. He is not beyond vanity, having made the effort to change his image from the dour, often crumpled and serious workaholic to a more fun-loving, relaxed, family man. But more important, he may yet find that, as the unexpected events of September 11, 2001, helped to define the presidency of George W. Bush and Britain's relationship with Washington, so he will find himself traversing uncharted waters.

He is assuming office with the British public wary of Labour politicians now in their third term in office, but still not enamoured with the Conservatives. That will buy him some time, but he will have a lot of work to do to win back the confidence of his people, even as he tries to keep the economy along the right path. Given all the loss of goodwill, it will be a daunting task trying to secure his own mandate for a fourth Labour term.

As he assumed office on Wednesday, he said it was time for the "change to begin". How skilful he will be at effecting change to some of the very policies he helped to craft and implement remains to be seen. In foreign policy, his commitment to having British troops withdrawn from the mess in Iraq will be difficult to implement logistically and diplomatically.

The personalities of Blair and Brown are markedly different; now the world waits to see whether this applies to the substance of policy rather than style. Yesterday's changes in Cabinet appointments suggests that Mr. Brown is indeed serious about implementing significant changes.