The ex-wife of Bryan Ferry has vowed to bring down the government, as she admitted her part in last week's pro-hunting demonstration.
Lucy Ferry and Jackie Coward "refused to move their cars".
Lucy Ferry took part in the demo in Parliament Square last Wednesday.
She was given a 12-month conditional discharge at Bow Street Magistrates Court in London after admitting obstructing the traffic.
"We can bring this government down. Brighton is next. We will keep fighting," she said outside court.
Ferry, who was also ordered to pay £40 court costs, said: "I am very angry and so are thousands of others."
Jackie Coward, 18, girlfriend of Mrs Ferry's son Otis, pleaded guilty to the same charge and also received a conditional discharge and was order to pay court costs.
The two women arrived for their appearance in court laughing and joking and dressed in three-quarter length tweed coats, sunglasses, scarves and woolly hats.
Prosecutor Hilary Ryan said: "At 6am on the day of the Countryside Alliance protest in Parliament Square, police were in the process of setting up cordons.
"As a police carrier came to a set of red lights, two vehicles appeared to park up at the lights.
"The defendants got out of the cars. They walked away so that when the lights turned green, the carrier was unable to proceed."
She said when police spoke to the two women, they refused to move their cars.
Coward said: "We were making a political statement and I was quite shocked at what happened.
"I'm surprised I have had to come back down here. I am a poor student from up in Newcastle."
The prosecutor said: "Both women are of previous good character."
The two women decided not to ask for a solicitor to represent them.
'Cooperation with police'
Asked if they had anything to say, Miss Coward said she had not been asked to move her vehicle by the police, as the prosecution suggested.
Mrs Ferry also disagreed with the suggestion that she had been uncooperative to police.
She said: "I certainly didn't refuse to answer any questions."
But she admitted that her car had been blocking the highway.
Police estimated there were between 8,000 and 10,000 protesters outside parliament on 15 September. But the organisers said there were 20,000.