The Brit singer was rushed to hospital just days after losing her baby.
Allen was six months pregnant when she miscarried the baby she had been expecting with boyfriend Sam Cooper.
She had been recovering at home in Gloucestershire but, according to a report in the Daily Mail, she was taken to hospital by ambulance on Friday.
Her spokesman confirmed: 'Lily Allen is back in hospital, where she is being treated for septicaemia. She is responding well to treatment and her condition continues to improve.
'Lily thanks everyone for their messages of support and again asks that she and partner Sam Cooper be left alone while she recovers.”