A pregnant woman has given anti-abortion protesters a piece of her mind outside a clinic in London.

The exchange was captured on video when a group called 'Abort67' got pulled up by a woman who certainly does not support the stance against terminating pregnancies.

The footage was uploaded to YouTube, where one pro-choice supporter called it "the best smack-down of anti-abortion protesters I've seen."

She took them to task for claiming they were not filming women using the clinic, even though members had video cameras strapped to themselves.

Expressing her distaste of a graphic poster tied to railings which showed a bloody foetus, the unnamed woman called Abort67's action "so wrong."

"You don't know why people are doing what they're doing," she fumed. "But you want to be out here judging and then filming."

As the anti-abortionists listened mutely, the woman went on to point out that abortions were sometimes chosen by women who had been raped. She said an abortion was preferable to an unwanted child being killed by its mother.

Watch the full exchange below [Warning: Contains strong language]: