Just as Sherlock Holmes observed in The Adventure of Silver Blaze, the most significant thing can be an absence — in the story, it was the dog that did not bark in the night-time. In the case of the US and UK governments’ efforts to tighten surveillance of internet users, the missing element is a ban on unbreakable encryption.

Both Barack Obama’s officials and David Cameron have barked about the subject, criticising companies such as Apple and Facebook for offering messaging applications that the security services suggest they cannot crack. But the US president and the UK prime minister have not bitten: neither has imposed a law to ban forms of encryption that criminals can exploit.

That is wise, for in pursuing a sensible goal — that the security services should be able to monitor the online activity of plotting terrorists — they were at risk of creating a practical mess. The bill unveiled by the UK on Wednesday does not ban companies from offering strong encryption, although they must be “reasonable” in handing over data.