"a group of gentlemen besieging a female Cabinet minister"

Fowles is not quite correct, although Punch's cartoon for this week in 1867 does refer to John Stuart Mill's proposal.  The text below the image is 'Mill's Logic; or, Franchise for Females.  "Pray clear the way, there for these - a - persons."'

The movement in support of giving women all the privileges of citizenship available to men was roundly mocked by Punch in ways very similar the cartoon described by Fowles.  Examples can be found here.

Mill's Logic, or Franchise for Females, from Punch (March 30th, 1867)
Public DomainMill's Logic, or Franchise for Females, from Punch (March 30th, 1867)