The law firm representing Britney Spears in her custody battle over her two kids has quit, claiming the pop star was "impossible" to work with.

The law firm Trope and Trope was Spear's third legal team in her battle with ex-husband Kevin Federline, who has won custody of the couple's two children due to Spear's erratic behaviour.

There has been a breakdown in communications between Spears and the law firm, "making further representation of her interests impossible", the firm said in court documents.

A court hearing to decide whether Trope and Trope will be relieved of their duties has been set for Feb 4.
The next hearing in the custody battle for Britney's sons is set for Feb 19.

The legal resignation came after Spears missed another court-ordered deposition with Federline's lawyer Mark Vincent Kaplan to undergo cross-examination about her parenting abilities.

Last month she called in sick to a similar meeting just hours after she was caught on camera at a nightclub.