Kevin Federline, Britney Spears' former husband, has subpoenaed staff at a rehabilitation centre the pop star attended as he tries to gain primary custody of the couple's children.

Federline's attorney served papers to an unidentified member of staff at the Promises treatment centre in Malibu. Spears checked into the centre in February after the breakdown of her marriage to the rapper.

Speaking to US magazine, Federline's attorney Mark Kaplan said: "An executive administrator from Promises rehab facility was served with a subpoena."

Kaplan added that his client was seeking "relevant information from all relevant sources" as he seeks to do all he can "to protect his kids".

The employee at the treatment centre is the fourth person who has been asked to testify about Spears' parenting skills. Previously, the star's assistant Shannon Funk, bodyguard Daimon Shippen and friend Alli Sims have been served papers requiring them to give evidence in the custody case.

A family court in Los Angeles will hold a hearing into the case in September, according to the magazine.

Federline, who met Spears while working with her as a back-up dancer, has concerns about the welfare of the two children from their three-year marriage.

On August 8th he filed for primary custody of 23-month-old Sean Preston and 11-month-old Jayden James in an LA superior court.

Spears recently finalised her divorce from her husband of three years and since the split she has engaged in bizarre behaviour such as attacking photographers with an umbrella and even shaving her head.

20/08/2007 07:23:13