Britney Spears has labelled her sister Jamie Lynn "scum" in another scathing Instagram post.

Britney Spears has branded her sister Jamie Lynn as 'scum' in a new Instagram post

Britney Spears has branded her sister Jamie Lynn as 'scum' in a new Instagram post

The 40-year-old pop star has been angered by her sibling's decision to release the tell-all memoir 'Things I Should Have Said', which has now become a national best seller in the United States.

Britney, who was freed from her controversial conservatorship last year, wrote on the social media platform: "The timing of your book was unbelievable Jamie Lynn... especially knowing the whole world had no clue what was really done to me!!!!"

The 'Toxic' hitmaker alluded to the fact that Jamie Lynn knows more about the conservatorship that she has actually disclosed.

Britney said: "My whole family including you is saying YOU DIDN'T KNOW.... B*******!!!

"The nerve of you to sell a book now and talk s*** but your f***ing lying. I wish you would take a lie detector test so all these masses of people see you're lying through your teeth about me!!!

"I wish the alimighty, Lord, would could come down and show this whole world that you're lying and making money off me!!!! You are scum, Jamie Lynn (sic)"

Britney previously labelled her sister as "f***ing hateful" and a "selfish little brat" after she questioned her decision to buy their mother a house after she had made it big in the music industry.

She wrote: "You selfish little brat!!! Saying how weird and dumb it was that I had bought a house for Mamma !!! She was so proud and you told that interview girl that it was just weird … LIKE I GUESS I WILL JUST WALK IN THESE HALLS … Why did you say that ??? ."