First of all, there are very few "British" usages that are not acceptable and used in the U.S. They tend to be in a higher "register," more formal, and more frequent in careful and educated speech. In my opinion and experience (U.S. native speaker, Northeast, in my sixties) all of the following would be natural and acceptable in U.S. English. "That's the biggest fish I ever saw." "That's the biggest fish I've ever seen." "That's the biggest fish I have ever seen." "That's the biggest fish I ever have seen." I think both usages can be found in the U.S. in both formal and informal contexts. Taking my cue from Susan612, evidence from song lyrics. Hmmm... as I collect examples, it's harder to find examples of the present perfect than I expected. Folk song: "The prettiest girl I ever saw Was sipping cider through a straw." Folk song: "Now once upon a time, there was a tree The prettiest little tree that you ever did see." Emily Dickinson: "I never saw a moor, I never saw the sea; Yet know I how the heather looks, And what a wave must be." Will Rogers: "I never met a man I didn’t like." Gelett Burgess: "I never saw a Purple Cow, I never hope to see one..." BUT: "I've Never Been In Love Before"--Frank Loesser, 1950s Broadway song title "I've never listened in among the sounds That a brook makes in such a wild descent"--Robert Frost "'If there's anything I do particularly despise, it's a lynching mob; I've never seen one that had a man in it.'"--Mark Twain, and within quoted dialog (a character's words) "“Yes, it will be lovely,” agreed Hinpoha. “I’ve 1 never lived in such a quiet place before. And I’ve never had you to myself for so long.”--1916 children's book, "The Camp Fire Girls at Onoway House"

I'll answer again, with a practical example. Say a child is coming to the dinner table to eat dinner. A parent in the UK would ask, so I am told: (BrE) Have you washed your hands (yet)? Whereas a parent in the US will ask: (AmE) Did you wash your hands? From context, it is clear to both child and parent that we mean: Did you wash your hands in preparation for dinner? (=BrE 'Have you washed your hands in preparation for dinner?) We AmE speakers *could* use the present perfect here, but we don't. Or at least, I never would, and neither would any AmE speaker that I know. Of course, a smart-alecky kid, or a teenager, might respond: "Yeah, I washed them yesterday." In which case, I (AmE) would still use the simple past and say "You know very well I meant did you wash them just now?"

I would classify that usage as informal, widely used, but not technically correct. I am reminded of a song I learned in Girl Scouts: The Littlest Worm The Littlest Worm I ever saw Was stuck inside My soda straw! (Repeat whole verse) He said to me Don't take a sip For it you do I'll surely flip! (Repeat whole verse) I took a sip And he went down Right down my pipe He must have drowned! (Repeat whole verse) He was my pal He was my friend But now he's gone And that's the end! (Repeat whole verse) That is the end There is no more Until I meet That worm once more! (Repeat whole verse)

We can say all the expressions with the present perfect. Often, or most often, we just feel free to use the simple past. http://separatedbyacommonlanguage.blogspot.com/2006/08/present-perfect.html?m=1 http://esl.about.com/od/toeflieltscambridge/a/dif_ambrit.htm http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv123.shtml

As someone from Australia, I find the use of the simple past in your example rather strange sounding (that is, the present perfect would seem far more apt...). I too have noticed this difference in tense usage and have wondered whether it is done for "dramatic/artistic effect" or whether it's actually grammatically correct in US English. A phrase I've heard several time is "That's the dumbest thing I ever heard". Perhaps the differences between American and British English lie beyond vocabulary, spelling and pronunciation!