A former metallurgy student who served as a junior Education Minister in James Callaghan's Labour Government in the mid-1970s, Ms Beckett, 63, with the rest of Mr Blair's Cabinet, has swung from the hard Left to a more accommodating centrist position in 30 years of politics.

Acting leader of the party after John Smith's death in 1994, Ms Beckett became the Secretary of State for Trade and Industry in 1997 before moving to the Department for the Environment and Rural Affairs in 2001.

Direct, scandal-free and unapologetic, Ms Beckett handled the foot-and-mouth crisis with a surety that won the respect of Tony Blair and the ire of farmers. Since then, she had a leading role in Britain's signing of the Kyoto Protocol, bringing Russia to the treaty and clashing with the Bush Administration

Richard Beeston explains: "Margaret Beckett will start work today with a daunting inbox, a set of issues that have been around for a while but which are all reaching crisis point.

"Top of the tray is Iran. Britain is leading the diplomatic efforts to rein in Tehran's nuclear programme - it's been one of the dominant themes of Jack Straw's recent administration - and now Beckett has to take over.

"Her first appointment is a meeting of the foreign ministers of the permanent five members of the Security Council on Monday to discuss a British-French resolution that would open the way to sanctions against Tehran. It's going to be difficult, complicated, a real diplomatic challenge and an unbelievably steep learning curve.

"Then we have Iraq. Where the formation of a new government is under way and Britain is preparing a large pull-out of troops, a delicate issue. In terms of the new government of national unity, the main posts have been filled and it's now a matter for the Iraqi Prime Minister to have his Cabinet approved by the rest of the government.

"Britain's role, only secondary to America's, is to help shape that process and make sure the right people are in the right jobs. Again, it's a challenging task, Beckett will have to very hands-on and yet subtle, with difficult personalities and enormous sectarian tensions to handle.

"Next is Afghanistan. Britain's is deploying 5,000 troops and taking on the Nato mission in the country with a very ambitious aim of pacifying the most unsettled parts of the country. There is a big expectation that British troops are going to suffer casualties and get involved in some very nasty fighting. This is a test of explaining a dangerous mission to the British public.

"Lower down on her agenda will be Darfur and the Middle East. Darfur is turning into a very intractable problem and, while Hillary Benn appears to be taking the lead on the subject, the Government at some point is going to have to start treating it as a political problem rather than a humanitarian crisis. As for the Middle East, Ms Beckett will have to continue the delicate, EU-led task of funding the Palestinian Authority while not being seen to recognise the new Hamas government.

"In all of these issues, the first step will be to establish a good working relationship with America. Britain's role in foreign policy increasingly appears as a bridge between the EU and the US and there is no doubt that Mr Straw dedicated much of his efforts to cultivating a close relationship with Condoleezza Rice, the US Secretary of State. Think of the Jack and Condi show, their visits to each other's homes. That's something that Ms Beckett will have to build from scratch and trust takes time. Typically, foreign ministers have to go through a couple of crises together before they can work very closely together.

"As for Jack Straw, I think he defied his critics, who thought he might not be up to the job. He handled a really difficult period -- the September 11 attacks, wars in Afghanistan and Iraq and, in recent months, Iran -- and he became a respected figure on the international diplomatic circuit. He may not have had the intellectual weight of his predecessor, Robin Cook, but he was less accident-prone and far more liked within the Foreign Office, where he was seen as an accessible, amenable figure.

"People will speculate as to why he has gone and most will suggest that he had fallen out with Tony Blair. Although much more foreign policy has flowed back from Downing Street to the Foreign Office in the last year, the marginalisation of Mr Straw during the last election campaign was interpreted as a loss of respect by Blair."

Times Recommends

• The real-life adventures of Tintin the spy
• Our universities face a radical upheaval
• Doctor Who