The father of Britney Spears will retain control over the once-troubled singer's personal and business affairs for an indefinite period, a Los Angeles judge has ruled.

Jamie Spears and a Los Angeles lawyer were first granted temporary control of Spears' affairs in February after the pop princess was twice hospitalised for psychiatric evaluation.

The conservatorship, which was set to expire on December 31, was made permanent by the judge at the closed-court hearing.

Spears can request it to be lifted at a later date.

Judge Reva Goetz said: "The conservatorship is necessary and appropriate for the complexity of financial and business entities and her being susceptible to undue influence."

Since February, Spears, 26, has turned around her life, reaching a custody settlement with ex-husband Kevin Federline, releasing a hit single Womaniser, working on a new album, winning three MTV Video Music Awards, and preparing for an expected first world tour since 2004.

Spears, one of the best-selling artists of the last decade, has been on the mend this year after making headlines for much of 2006 and 2007 for shaving her head, going to a rehabilitation centre, partying without underwear and wearing a pink wig.

Last week, Spears escaped a criminal conviction for driving without a California licence in 2007 after a Los Angeles jury deadlocked 10-2 in favour of an acquittal. A guilty verdict would have given Spears a criminal record.

© Independent Television News Limited 2009. All rights reserved.