The singer, who beat Jahmene Douglas to the title last night (9th December), went straight to the top of the download chart with winner's single Impossible, after it was released at midnight.
Before learning of James' chart debut, she had tweeted: "SOOO much love to all of our UK fans for supporting the song. Love you all."
In a message to collaborator Will, Britney also said: "Hearing #ScreamAndShout is #1 on iTunes in the UK. @iamwill, are you over there buying up tons of singles ;)."
However, Spears' chances of scoring her first UK No.1 single since Everytime in 2004 looks unlikely thanks to Arthur's already apparent chart success.
Fans of the Middlesborough singer can also expect James' debut album soon, with the star recently claiming that he wants it released "as quickly as possible", adding to Daybreak: "I'm not gonna wait around. I've got a lot of material ready to go now."
Syco is donating 100% of the profits from each download and CD sale of Arthur's single - estimated at £1 per CD and 20p per download - to children's charity Together for Short Lives.
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