[joshka]

The uk law states you'd still have to disclose that these keys existed.

Where, in a case in which a disclosure requirement in respect of any protected information is imposed on any person by a section 49 notice—

(a)that person has been in possession of the key to that information but is no longer in possession of it,

(b)if he had continued to have the key in his possession, he would have been required by virtue of the giving of the notice to disclose it, and

(c)he is in possession, at a relevant time, of information to which subsection (9) applies,

the effect of imposing that disclosure requirement on that person is that he shall be required, in accordance with the notice imposing the requirement, to disclose all such information to which subsection (9) applies as is in his possession and as he may be required, in accordance with that notice, to disclose by the person to whom he would have been required to disclose the key. (9)This subsection applies to any information that would facilitate the obtaining or discovery of the key or the putting of the protected information into an intelligible form.