This seems like really poor journalism to me. While it does sound like Arrington lost the libel case, I believe it was a default judgment since Arrington didn't defend himself, while this article makes it sound like the court ruled that he was guilty as accused. Also, it doesn't sound like the court has awarded any damages yet, so I doubt he's currently at any risk of being arrested for failure to pay.
Is this really true? IANAL but debt collection in the UK is particularly difficult even if you've received a legal judgment. Perhaps it's different for non-nationals, but even if you win a judgment at court against someone, you have to then get warrants and all sorts to pull it off.