Rosena Allin Khan, who also works as an A&E doctor, tweeted the warning after police stepped in to end an unlicensed rave last night on Tooting Bec Common.
Uniformed officers also used dispersal zones to give them extra powers to end a second unlicensed event on Clapham Common.
Elsewhere, four people have been charged after a rave in Brixton on Wednesday, that resulted in 27 police officers being injured after it turned violent.