[brzz]

Yeah, I would assume the worst from the UK government on these things.

I hadn't heard of the French double-anonymous system, though. That does sound slightly better.

[feurio]

If a site creates some opaque token representing the request, and the token is signed by the ID service with no other information disclosure that "The user that presented this is of the appropriate age" that would seem like a reasonable compromise.

Token could be signed out-of-band to obscure the interaction between the parties.