It was only when Mr Cook sat down in a small room at United Nations headquarters that he realised the deal that had been under negotiation for almost six months was at last in the bag. "Until then, it would only have taken one phone call from Tehran and it would have been over," one British official conceded last night.
More than 3,000 miles away, anxiety was running even higher inside the Foreign Office where Rushdie and some of his closest supporters were awaiting the word from New York. Would his nightmare end at last?
Last January the first clue emerged that progress might be possible. Mr Cook made a speech in Washington that contained unexpectedly warm words about Iran and its new moderate President, Mohammad Khatami.
Mr Cook recalled yesterday how he was trying to signal that it was time to "encourage the new signs of glasnost in the government of President Khatami and that isolation may not be the best way in which to address those parts of the Iranian government and state that give us concern". Britain then used its presidency of the European Union to encourage dialogue.
The negotiations about how to end Rushdie's plight started in the spring. Already, Tehran had made verbal promises not to act on the fatwa. But the Foreign Office wanted a formal, and written statement to that effect. It was also pushing for Tehran to dissociate itself from the $2m (pounds 1.2m) bounty placed on Rushdie's head by the Islamic militant Khordad Foundation.
Far from the eyes of the media - and from those of President Khatami's hardline opponents in Tehran - those negotiations were first held by foreign ministry officials in a third, unidentified, country. Soon, however, they were taken up in Tehran itself, channelled through Nick Brown, the British diplomat who has been there as charge d'affaires since last year.
As hopes rose that a deal might be possible, plans were slowly laid for a meeting between the foreign ministers. No such meeting had taken place since 1994 when Douglas Hurd was Foreign Secretary. This week's gathering of ministers for the UN General Assembly seemed perfect.
Normalisation of diplomatic relations between Britain and Iran will have repercussions in a host of fields from trade to the fight against international terrorism and drugs trafficking, and - by hastening Iran's return to the international community - could affect the strategic situation in the Gulf.
For Rushdie it means a tentative return to the life from which he has been largely exiled for nearly 10 years.
Rushdie was the darling of the literary luvvies when his life was blighted by the fatwa.
He vanished from a life where he was feted as the 1980 Booker prize-winning author of Midnight's Children, where he could have had every expectation of accumulating more wealth and success.
In the past nine years, he has, instead, endured an exhausting schedule of keeping on the move, enduring 50 different lodgings in the first five months alone.
His second wife, Marianne Wiggins, an American writer, left him after 15 months in hiding, and he has been forced to learn the language of diplomacy as he badgered politicians to fight his cause.
At his lowest ebb, in 1990 the desperate Rushdie even announced he was embracing Islam as a conciliatory gesture to Iran, a move he later regretted. But he has also received great support from many who, even when the writer himself proved difficult and arrogant, defended to the hilt his right to free speech.
Frances de Souza, the free speech campaigner, led the Salman Rushdie Defence Committee, which gave public voice to the author's plight when it was too dangerous for him to appear in public.
It has been a long, strange chapter in a remarkable life. Salman Rushdie was born to a middle-class Anglophile family in Bombay in 1947. They dispatched him to Rugby School at the age of 13 where he was the victim of racist bullying, before going on to Cambridge.
After dabbling in fringe theatre, he became an advertising copywriter for 10 years, coining the cream cake phrase "Naughty but nice", married Clarissa Luard and became the father of a son.
Zafar was his best man when he married for the third time last August to Elizabeth West, a publisher. Rushdie now has a second son, Milan. And for the first time in a decade, he may get a chance of a normal family life.