Britney Spears Dashcam Shows Cops Cuffing Her After Failing Sobriety Test

We're seeing the moment Britney Spears tried -- and failed -- taking a sobriety test and was cuffed by cops during her DUI bust ... in new video obtained by TMZ.

We've obtained dashcam footage from Britney's March 4 arrest ... which shows cops questioning her after pulling her over for allegedly swerving through lanes.

At one point, after officers walked her out of frame, you can hear Britney ask if they took her phone ... but they reassured her it's still in her purse.

As you know, police say they noticed the "distinct odor of an alcoholic beverage" on Britney, according to the police report of her arrest.

The officer claims Britney admitted to drinking one mimosa hours beforehand but said ... "I could probably drink four bottles of wine and take care of you. I’m an angel."

At one point, officers say Britney claimed to be a "zero" on the sobriety scale, the cop claims, although the police report also notes Britney told the officer she'd popped Adderall, Prozac, and Lamictal -- a mood stabilizer and anticonvulsant -- that same day.

The cop says Britney blew under the legal limit on 2 breathalyzers at the station ... according to the police report.

As you know ... police dispatch audio revealed concerned drivers called in after seeing her driving erratically.

Britney cut a plea deal with prosecutors earlier this month, and the DUI charge was reduced to a so-called "wet reckless" -- meaning a reckless driving offense involving alcohol.