Can someone who knows tell us what UK 'Restricted' classification equates to. In the US 'Restricted' is used with both unclassified information 'For Official Use Only-Restricted Limited Distribution' and with restricted circulation of classified as in Secret/US/UK Only.
The article says this document was given to family members. In that case, if it were in the U.S., the highest classification is could have would be FOUO, if that.
Letting something like that out into public isn't good, but it's hardly a leak of real significance. Sounds like the newspaper is just trying to hype this story.