Britney Spears has branded her sister Jamie Lynn as "scum" in another furious rant.Toxic singer Britney, 40, hit out at her younger sibling Jamie Lynn, 30, as she shared a clip of The Real talkshow hosts discussing Jamie Lynn's recent book release.The talkshow hosts were seen defending Britney in the clip as one says: "If you wanna clear your name who is it important to clear your name to? Your sister or the masses of people?" Britney then hit out at her sibling in the caption as she wrote: "National best seller ???? DUH Get exclusive celebrity stories and fabulous photoshoots straight to your inbox with OK!'s daily newsletter. You can sign up at the top of the page.