I know you want to err on the side of caution, but that's not 100% accurate.

Only "obscene" lolicon is illegal in the US. Here's the relevant definition from 18 U.S. Code § 1466A:

(1)
   (A) depicts a minor engaging in sexually explicit conduct; and
   (B) is obscene; or
(2)
   (A) depicts an image that is, or appears to be, of a minor engaging in graphic bestiality, sadistic or masochistic abuse, or sexual intercourse, including genital-genital, oral-genital, anal-genital, or oral-anal, whether between persons of the same or opposite sex; and
   (B) lacks serious literary, artistic, political, or scientific value;

And (2) has already been invalidated for not requiring the full Miller Test.

Britain's law has a broader definition of offensive and lacks any kind of artistic value defense or requirement that the work be considered as a whole. Though it does exclude images that are part of classified works (i.e. movies previously approved by the censorship office) as long as they have not been extracted from it.