The Oscar-winning actress signed a petition to free Polanski, who has been imprisoned since September (09) on the request of Los Angeles law officials.
But on a trip to Exeter University in the U.K. earlier this month (Nov09), Thompson was accosted by a student who requested she retract her support.
And after a lengthy chat with Caitlin Hayward-Tapp, who has set up a petition for those opposed to Polanski's freedom, Thompson agreed.
The 19 year old says, "I asked if I could speak to her (in person). She is such an inspirational woman, I reckoned she must have been willing to reconsider.
"It turned out she was very willing to hear what I had to say. She said she knows Roman Polanski and that she had had calls from friends asking her to sign the petition. She knows what a terrible early life he (Polanski) had.
"She said she had already been thinking a lot about the petition, as others had expressed their dismay at her signing it. We talked for 15 minutes and by the end she said she would get her name removed. She said regardless of the fact she knows him and the terrible things he has been through, a crime is a crime. If she doesn't do this, it'd be a great shame."
Polanski is facing extradition to the U.S. to face sentencing over a 1977 charge of unlawful sex with a 13-year-old girl. He pleaded guilty to the charges but fled the country in 1978 before he could be handed his punishment.
Despite calls from his victim to drop the case, Polanski has been refused bail on two separate occasions over worries he is a "flight risk".