Britney Spears' new lawyer Mathew Rosengart, has declared he's working "aggressively and expeditiously" to have her father, Jamie Spears, removed from her conservatorship.

Rosengart is a former federal prosecutor who has previously worked with Sean Penn and Steven Spielberg. He was appointed Spears' lawyer last week, after a judge granted the singer permission to appoint her own legal representation in the battle over her conservatorship.

Spears said she approved Rosengart after several conversations with him. Samuel Ingham III had served as her court-appointed legal counsel since the beginning of her conservatorship in 2008, as Spears was previously deemed incapable of appointing her own lawyer.

Ingham stepped down in the wake of Spears testimony last month, during which she criticised him and others involved in her conservatorship, particularly her father.

Following a brief hearing on July 19th, Rosengart told reporters that he and his firm, Greenberg Traurig, LLP, were working “aggressively and expeditiously” to file a petition for Jamie’s removal from the conservatorship.

In a statement, he said: "First, I once again want to thank Britney Spears for her courage and for her strength. I want to thank Judge Penny for her courtesy and welcoming my firm and I into this case, and I also want to thank Britney Spears' fans and supporters.

"The outreach and support for my firm, myself and most importantly Britney has truly been overwhelming – coast to coast and literally throughout the world.

"As I said in court last week and outside, my firm and I are moving aggressively and expeditiously to file a petition to remove Jamie Spears, unless he resigns first."

During last week's hearing, Rosengart questioned Jamie’s motives behind remaining as his daughter's conservator. "There’s a real question as to why Mr. Spears does not voluntarily step aside today," he said. "Does anybody really believe that Mr. Spears’s involvement in the case is in the best interest of Ms. Spears? If he loves his daughter, it is time to step aside, so she can move forward."

He has also called into question whether the conservatorship should ever have been put into place back in 2008, and said he and a team of attorneys from his firm would be taking a close look at the details of the arrangement.

Lawyers for Jamie Spears said he would not be stepping down as Rosengart challenged, adding that he has only ever had his daughter’s best interests in mind.

Jamie's lawyers have also questioned the accuracy of Britney’s claims of “conservatorship abuse”, which the singer said she wanted her father charged with.

After Spears harshly criticised her father in her testimony, his lawyers filed for an investigation into the claims she made, questioning the actions of both Ingham and her current personal conservator Jodi Montgomery

The filings, made on July 1st in LA, stated that "it is critical that the Court confirm whether or not Ms. Spears’s testimony was accurate in order to determine what corrective actions, if any, need to be taken."

He has also denied that he was the one in control of his daughter, pointing out that Jodi Montgomery had been his daughter's personal conservator since September 2019, however, many of Spears' claims of abusive behaviour predate Montgomery's appointment as her conservator.

Spears' explosive June 23rd testimony was the first time she has ever spoken freely and publicly about her 13 year conservatorship. She described how she had been forced to perform and to take medication against her wishes, that she wasn't permitted to remove her IUD and called her conservatorship is 'abusive'.

Along with Ingham, her testimony prompted the resignations of her long-time manager Larry Randolph and the financial firm Bessemer Trust, who were co-conservators of her estate along with her father.

It has also prompted two members of US Congress, Republican Nancy Mace and Democrat Charlie Crist, to propose a bill to reform the system.

They have put forward legislation that would allow Spears and other conservatees to request their judge-appointed conservator be replaced with either a public guardian designated by the state, a family member or a private agent.

Currently, those in conservatorships must prove in court that fraud or abuse has occurred to have their conservator replaced.

The Freedom and Right to Emancipate from Exploitation Act, or FREE Act, would remove this requirement, allowing Spears to make another request to remove her father as conservator without having to prove abuse or fraud.

The judge presiding over Spears' case, Brenda Penny, denied a ‘months-old’ request to remove Jamie as her conservator at the end of June, which had been submitted by Ingham. She did not however, rule out future petitions for his removal or suspension.

"We want to make sure that we bring transparency and accountability to the conservatorship process," Mace said in an interview with Crist.

"The Britney Spears conservatorship, it’s a nightmare. If this can happen to her, it can happen to anybody."

Spears posted on Instagram recently, saying she has no plans to perform again while her father is involved in her conservatorship.

The next hearing date for Spears' conservatorship case is September 29th.