[elliott99]

"However, it is long-standing government policy that pardons under the Royal Prerogative of Mercy should be reserved for cases where it can be established that the convicted person was innocent of the relevant offence, and not to undo the effects of legislation which we now recognise as wrong."

In this case, I guess pardon is not appropriate. I think the way we think of pardons at least in the US, is your first sentence, in which case Turing should definitely be pardoned.