Re: Mrs May is TAPS (thick as pig . . . )
"Isn't there a single person in No 10 who can explain that this kind of secret cannot be kept secret?"
You have probably never worked for a medium/large company, or government, or at least have not had to deal directly with very senior management/officials.
PM May almost certainly has no one who reports to her, nor anyone who reports to her reports, with any crypto background, and possibly no one with any hands-on tech background.
Some outsider or low-level functionary who comes in with a claim like that is easily dismissed, as obviously boffins find solutions to previously impossible problems all the time, so how can it be true? Anyone who disagrees is not a "team player", so all those direct and second-level reports nod their heads wisely in agreement, and the claim is ignored. Happens all the time. Hans Christian Anderson even wrote a story about that "team player" managerial mentality, called "The Emperor's New Clothes".