You are right, not only that but also the title of Knight ceases when one dies.

There are honours that do not expire, I'm sure something relevant can be found.

Though I think the fact we understand and appreciate the full magnitude of what he achieved in the time he had (even some of the general public with little technical interest are at least aware of his contribution to the war effort if not his contribution to information/computation/intelligence theory) is probably the best honour we can give him.

Give him an Oscar then.

A posthumous... wait for it... Turing Award.

I am saddened none of the media used the headline, "Turing Complete!"

An Oscar hardly seems like a fitting British commendation for someone that isn't an actor or director.