Question regarding the Official Secrets Act.
DC would have signed it, surely he would have. It must be a rule that working within No10 you have to sign it.
Therefor any media sent by, or corresponding to, the PM must come within that Act.
The Parliamentary Committee charged him with coming up with evidence to substantiate his claims, which (made to a Select Committee) would not contravene the OSA.
Also - I very much doubt that any of the content of today's release could be construed as breaching official secrets.