Lily Allen has threatened to post Katy Perry's phone number on Facebook if the singer bad mouths her again, according to reports.

Perry is understood to have angered Allen recently when she described herself as “a fatter version of Amy Winehouse and a skinner version of Lily Allen”.

Allen later responded by saying Perry was a “crass” American version of her, prompting the singer to apologise about her weight comments.

Allen is now reported to have threatened to reveal Perry's phone number on the social network if she makes any more comments.

“I have Katy Perry’s number, someone did me a favour,” Allen is quoted as saying by the Sun newspaper.

“I’m just waiting for her to open her mouth one more time then it hits Facebook.” 

Allen is also reported to have joined two anti-Perry groups on Facebook - I hate Katy Perry and her dumb-ass song I Kissed A Girl and Katy Perry? Who in the hell does she think she is?.

Allen is due to release of her second album, 'It's Not Me, It's You', next month.

Lily Allen and Katy Perry