Climate change security threat

She will determinedly set out a long-term strategy amid suggestions her job could be among those at risk if, as expected, Chancellor Gordon Brown becomes Prime Minister.

Mrs Beckett will address the Royal United Services Institute (RUSI) shortly after Tony Blair is due to announce he is stepping down as Labour leader, paving the way for Mr Brown.

She was singled out by Tory leader David Cameron on Wednesday as one of those "for the chop" in a shake-up of senior cabinet positions once Mr Blair has departed 10 Downing Street.

But Mrs Beckett gave no quarter to his speculation, announcing she was planning a seminar to discuss the issue and speaking of "the foreign policy that I will pursue".

She will say: "I simply do not believe that we will solve the security issues of the day unless we address the global insecurities that underlie and exacerbate them.

"And I do not think that I would be doing my job properly if I considered it enough simply to respond to each crisis as it occurs: the foreign policy that I will pursue is one that looks down the line at how we can prevent such crises from happening at all."

Mrs Beckett will suggest there has been a sea-change in the international system on the climate change issue, with more nations recognising its importance.

Last month she brushed aside objections from developing countries to make it the subject of a groundbreaking debate at the UN Security Council in New York.

Using Britain's Presidency of the Council to force the subject to be discussed, she said there were "few greater potential threats to... peace and security itself."