The 'Sheezus' singer took to the social networking site to vent her anger after the former 'The Apprentice' star called her a ''short-arse mother in big pants''
Katie wrote the harsh remarks - which were later tweeted by a magazine - in her column for The Sun newspaper after Lily posted a topless video of herself dancing in spanx underwear earlier this week.
Lily wrote: ''@OK_Magazine @KTHopkins honestly defines unnecessary, as does this article, as does your magazine. Both everything that's wrong with humanity.
''Fat shaming, woman hating, moral high ground f***tards. Just stop your pathetic existence, you do nothing.......for anyone srlsy.''
The 29-year-old mother of two launched a further attack on the columnist, relaying an incident in which Katie, 39, was photographed naked during a romantic encounter in a field.
She wrote: ''@KThopkins tipping off the paps that you'll be f***ing someone in a field = unnecessary, also deluded and self important. #begone.''
Katie replied: ''but least I didn't film myself doing it & I had someone else to hold my arse in for me.''
Lily continued: ''@KTHopkins sure, I bet those paps were just hanging out in some suburban field and happened to stumble upon your 'romp'.''
Katie then shared a photo of Lily holding her breasts, with the caption: ''Field or no field, least I have someone to hold my boobs for me @lilyallen PS your kids asked who was in this photo.''
Lily then wrote her final reply: ''@KTHopkins stay classy babe.''
It isn't the first time Lily and Katie have become involved in a bitter Twitter feud. The pair battled it out on the social networking site after Katie attacked the singer for putting on weight following a miscarriage earlier this year.
This Doctor won't be saying 'goodbye' in the same way as those who have left the series in recent years.