As someone who works with 'restricted' documents, I can confirm they're very dull. The worst fallout from this particular slip-up is going to be heads of security across the civil service getting their knickers in a twist and creating more and more ludicrous 'security procedures'.
This, in turn, will lead to silly spending on daft 'precautions'.
No-one cares, apart from the Daily Mail and a handful of people who's jobs depend on making it all seem important. You, me, and everyone else will still have to pay for it, though.
(anonymous ('confidential'?) for obvious reasons, and Paris because even though it's often concealed, what's underneath isn't exciting at all.)