Robertson to step down as Nato's Secretary General

George Robertson, the secretary general of Nato, took colleagues by surprise yesterday by announcing he will quit in December after rejecting a request to stay in office for another year.

The move leaves the question of his successor wide open, and fuelled speculation that Lord Robertson of Port Ellen may be destined for a return to politics in Edinburgh or Westminster. The former secretary of state for defence said he had "been asked by a number of governments to stay on, but I believe four years is the right term in this demanding and onerous job and I'm looking forward to another full and active year ahead before I go."

One Nato diplomat said that Lord Robertson felt the tasks he set himself at Nato had been achieved, and there was a "range of possibilities" for the future. "He's certainly not going into retirement," he said.

Lord Robertson, a close ally of Tony Blair, could expect to be given a ministerial post in the Lords, or alternatively might stand for the Scottish Parliament in the hope of becoming First Minister. But the path to the top job in Scottish politics looks difficult and Lord Robertson, 56, may prefer to work in the private sector.

Nato officials are already speculating about possible successors with Aleksander Kwasniewski, President of Poland, a potential candidate. But the timing is bad for Mr Kwasniewski, whose presidential mandate expires in late 2005. He said yesterday he had "no intention of assuming any other responsibilities whether they are in Poland or abroad". Other names mentioned include the former prime ministers Antonio Guterres of Portugal and Wim Kok of the Netherlands, and Norway's Defence Minister, Kristin Krohn Devold, who could become the first woman to lead Nato.

Lord Robertson needed some persuasion to accept the job, which he took up in October 1999. During his tenure Nato put new focus on improving its capabilities, successfully managed a Balkan crisis, agreed to a big expansion of members and forged a new link with Russia.

But Washington's sidelining of Nato during the war in Afghanistan, and splits in the alliance over the prospect of a US-led war against Iraq, led to Nato's role in international security being questioned.