My sister S whispered over the telephone that she’d heard about a woman from County Durham, now living in Sydney, who had sold secrets about British coal-mining to the Chinese.

When I next saw her in person, my sister confided that she now feared for her own life because she had unwittingly passed on this ‘classified information’. In response I whipped out a copy of a library book that featured a glossy picture of Sydney opera house on its front cover.

‘Don’t be daft’, I said. ‘She’s already published the entire story here’.