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Sorry douglas, I didn't realise there was a time limit for answering. Thank you all for your replies and suggestions. Yes, the book is Atoms and Ashes by Serhii Plokhy. In the great scheme of things the mistake isn't large but I believe that if you're going to write a factual book at least get the facts right. On Page 128 he writes " The weapon was dropped off the tip of Christmas Island, Britain's usual testing ground in the Indian Ocean off the Australian coast, by a British bomber at 8:47 pm local time on Friday, November 8, 1957."
Britain's nuclear testing was on Christmas Island (now Kiritimati) in the centre of the Pacific Ocean, a thousand miles south of Hawaii and about 4 thousand from Australia. The Americans also carried out a series of tests there in 1962 under operation Dominic.