Britney Spears' custody battle could cost her over $700,000. The troubled singer's lengthy court process with ex-husband Kevin Federline to establish access rights to their sons, Sean Preston, two, and 23-month-old Jayden James, led to two law firms billing her a combined total of $466,000, court documents have revealed.

In addition, Britney, 26, also agreed to pay Kevin's legal fees, which amounted to around $250,000. The largest bill comes from attorney Stacy D. Phillips, who claimed in court filings that she is owed nearly $407,000 for four months of work and says she has written off an additional $125,000 in fees.

The remainder of Britney's bill is for $60,000 for two months work from Laura Wasser who took over the case in June. She brokered the agreement between Britney and Kevin that saw him retain full custody while the singer has visitation rights.

Phillips claims the case was more complicated because Britney's father Jamie, as co-conservator of her estate, has control over Britney's affairs.

The payments have to be approved by the Los Angeles commissioner and lawyers for Britney and Jamie have indicated that they will contest the bill.

A hearing has been scheduled for September 16 to discuss the fee. Britney and Kevin married in 2004 and their divorce was finalised last July. Under the terms of their divorce settlement, the singer currently pays her ex-husband $20,000 a month.