Troubled star Britney Spears has apologised for attacking a paparazzo's SUV with an umbrella earlier this year - insisting she was "rehearsing for a film role".

The Toxic singer has attributed her bizarre behaviour outside estranged husband Kevin Federline's house - the night before she entered rehab in February - to preparation for a part in a movie about a much maligned wife who swaps places with her husband.

In a message to gossip site X17, she writes: "I want to apologise for the past incident with the umbrella. I was preparing a character for a possible movie role where the husband doesn't play his part so they swap places.

"Unfortunately I didn't get the part. I'm sorry I get carried away with my role!"