HOWEVER good Margaret Beckett is at speed-reading on a plane it is hard to see her wielding the authority that Jack Straw would have had last night in New York, in the latest talks on the Iranian crisis.

Her debut as Foreign Secretary on the tiny, airless stage of this drama, where a small cast of ministers has battled for four years to talk Tehran down from its nuclear ambitions, comes as the heat is rising.

In Tony Blair’s Cabinet reshuffle, the replacement of Straw with Beckett still stands out as the big surprise. The temptation (in Iran even more than Britain) has been to say that Blair put her there to take a tougher line. That seems unlikely, or at least, an exaggeration. Straw’s approach was well-judged — until the Iranian regime changed — and he did have the merit of experience. The last thing he needs now is compliments from Tehran. All the same, Iranian hardliners have been noisy in their mourning for his exit.

“Mrs Beckett, contrary to Straw, is famous for being totally loyal to Tony Blair,” said a commentary in the conservative Jam-e Jam newspaper yesterday, It praised Straw for his “independence” from Blair (and warned him that Robin Cook, whom it said was “dismissed” as Foreign Secretary for the same quality, had met “ultimately...with (a) suspicious death”).

True, Straw had said for months that taking military action against Iran would be wrong (once, over-quotably, that it would be “nuts”). But if Blair thought this was a serious divergence from his policy he could presumably have told his Foreign Secretary to shut up.

The real reasons for Straw’s move were surely subtler: springing from the prominence and, all right, “independence” that a minister gets after five years in the job. Straw’s friendship with Condoleezza Rice, the Secretary of State, was too photogenic; the anecdote of her giving up her bed to him on the flight to Baghdad more memorable than their efforts when they arrived.

As it happened, they met Ibrahim Jaafari, then Iraqi Prime Minister, whose refusal to step down was blocking the formation of a government. On Straw’s return, he joked — in an interview with The Times — that the desire of prime ministers to cling to power was not confined to Iraqis.

That was the quip of a confident man — perhaps too much so. It is not hard to see that kind of thing needling a touchy Prime Minister.

Straw, who tells good jokes, generally deploys them to more calculated effect. His best, perhaps, was at the United Nations in the run-up to the Iraq war. He rebutted a grandiose speech by Dominic de Villepin, then French Foreign Minister, by offering that Britain “is also an old country, founded by the French in 1066”. It broke the tension (although it didn’t win agreement on the war). He said later that he had considered saying “invaded by the French” but that “humour needs to be inclusive, and so I changed it”.

But that technique of familiarity has attracted critics, not least on his approach to Iran. Some argue that he tried to build relations where frostiness would have been appropriate. He started visiting Iran early in his tenure, and it was a region that Blair left to him. The visits earned him the tag “Tehran Jack” from British critics — and “Ayatollah Straw” from Iranian reformers, who felt he gave too much support to the clerics’ regime.

But his approaches had at least laid the ground for talks when details of Iran’s covert nuclear programme broke in 2002. In the initiatives put forward by the trio of Britain, France and Germany in rounds of talks in Tehran, Vienna and Geneva, he became the elder statesman, as the other ministers changed.

There is some value to experience in these talks. They are showy; the two sides sit face to face across a narrow table, broken by huddles in the garden. Adroitness in judging the Iranians counts for something; so does understanding of nuclear techniques — and a good memory for four years of rejected offers and broken promises. The British tactics showed some signs of working until the election of a new, hardline Iranian government last summer.

Beckett has the advantage of newness. Iran does not know what to expect. But at this crucial point the talks might have gained more from Straw’s experience than from the arrival of a novice assumed to be speaking with her master’s voice.

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