… is from pages 543-544 of the 1988 collection of Lord Acton’s writings (edited by the late J. Rufus Fears), Essays in Religion, Politics, and Morality; specifically, it’s a note drawn from Acton’s extensive papers at Cambridge University; (I can find no date for this passage) (brackets original to Fears):
[It is] the first quality of a Liberal to claim the same thing for others and for oneself, to dislike exception and prerogative, to think of all men and all countries, to acknowledge the rights of the individual, derived from nature and universal, in preference to the primitive rights of a country or of a clan, obtained by force and not from heaven.