The Prime Minister is to become a Dalek in the new series of Doctor Who. PM Harriet Jones, played by Penelope Wilton, will pose a threat to the Time Lord – as the mother of all Daleks, according to The Sun. Fans last saw her two years ago in The Christmas Invasion, when she was brought down by the Doctor, played by David Tennant, for being ‘too cocky’. She was later ousted when The Master brainwashed voters into putting him in Downing Street under the alias Harold Saxon. In a shock moment, the casing of one of the metal monsters opens to reveal the ex-PM has been converted into a tyrannical pepperpot. A source said: “It’s a stunning highlight of the series. Penelope was smuggled on to the set to try to keep the storyline a secret.” Also in the show, classic enemy Davros, played by Julian Bleach, returns to build a new race of Daleks after just one, called Caan, was left alive last year. The fourth series of the sci-fi hit, which returns to BBC1 in the spring, sees the Doctor helped by four assistants. Catherine Tate and Billie Piper return as Donna Noble and Rose Tyler, and Elisabeth Sladen is back as Sarah Jane Smith. Freema Agyeman, who recently starred in Doctor Who spin-off Torchwood, returns for four episodes as Martha Jones.