The newspapers are currently full of the story of how, allegedly, Markers award students for writing obscenities on GCSE papers. The main point has been well thrashed out (it seems to gone unnoticed by those so outraged that even being awarded marks, the result for the student who only wrote "f*** off!" was still a resounding Fail). But I was particularly interested in one of the linguistic points mentioned by Arnold Zwicky at Language Log (Test obscenity, taboo avoidance, and prescriptivism): the subsequent criticism of chief examiner Peter Buckroyd for commenting "It’s better than someone that doesn’t write anything at all" (as opposed to "someone who").
The idea that using "that" for persons is an error is a common language peeve, and Zwicky goes into its role as a piece of usage mythology. He notes that it's a usage that MWDEU demonstrates to be standard" ... see the citations under That 2 on page 895, which show the objection to be, typically for this sort of thing, a concoction by 18th century grammarians ... "and which even Paul Brians, in Common Errors in English Usage, classifies as 'non-errors'". In case of objections that these are US sources, a quick skim of English literature finds examples going way back.
*"the man that handleth the scorpion" (Geoffrey Chaucer, The Canterbury Tales)
* "a woman that feareth the Lord" (Proverbs 31:30, King James Bible)
* "Then I saw the Man that sat upon the cloud" (John Bunyan, Pilgrim's Progress)
* "The man that hath no music in himself" (William Shakespeare, The Merchant of Venice)
* "While I stood thus amusing the Lady that was with me" (Daniel Defoe, Roxana)
*"The Lass that Made the Bed to Me" (Robert Burns)
* "He, the most excellent Man that can be imagined" (Jane Austen, Plan of a Novel)
* "I am the girl that dragged little Oliver back to old Fagin's" (Charles Dickens, Oliver Twist)
* "The lady that was here last night" (Charles Dickens, Bleak House)
*"The Woman that Lives without Eating" (Rev. AD Milne)
* "The Man that was Used Up" (Edgar Allan Poe)
* The Man That Corrupted Hadleyburg (Mark Twain)
*"HMS Pinafore; or, The Lass that Loved a Sailor" (Gilbert & Sullivan)
* "The man I want to meet is the man that Candida married" (George Bernard Shaw, Candida)
* "The Girl That I Marry" (Irving Berlin)
*"she was also someone that millions of girls living hum-drum lives loved to identify with" (Betty Grable obituary, The Times, Wednesday, Jul 04, 1973).
With so many examples in prestigious sources, "that" for persons can hardly be called wrong. It may be a minority usage, but that can be tested. It's one of the many neat features of Google that nowadays corpus analysis is within anyone's grasp. There's bound to be some degree of bias: online sources naturally under-represent recent in-copyright books, and it may be impossible to separate out hits that don't cover the context required (in this situation, "that" as a relativizer). But as a rough-and-ready test, it's easy to get a broad idea of the frequency of usages: for instance
Global: "someone that" 18.2m / "someone who" 97.7m / 1:5.36
UK: "someone that" 0.647m / "someone who" 5.53m / 1:8.55
"That" as a relativizer for people, then, appears rather less common in the UK than globally, but descriptively speaking, it's still well within normal variation.