Aliens of London

The Doctor returns Rose back to Earth in the TARDIS, but miscalculates, ending up 12 months after he first left with Rose instead of 12 hours. As such, Jackie, Rose's mum, is furious with the Doctor, and Rose's boyfriend, Mickey is upset as he was suspected of murdering Rose. While Rose expresses her frustration to the Doctor of not being able to tell the truth of where she's been, they witness a spacecraft crash through Big Ben and fall in to the River Thames. Central London is shut down while its population become excited at the possibly of first contact with an alien species. The Doctor suspects trickery, and uses the TARDIS to land where the alien craft and its pilot has been taken. Along with Dr. Sato, he discovers that the alien craft was launched from Earth, and its pilot was nothing more than a Earth pig, modified by alien technology.
Meanwhile, the government is unable to locate the British Prime Minister due to the confusion of the crash, and MP Joseph Green is named acting Prime Minister at 10 Downing Street. However, Green is revealed to be a Slitheen, a calcium-based alien species that compress their bodies into large human "suits" resulting in frequent releases of flatulence, along with two other high members of the government, Margaret Blaine of MI5 and Oliver Charles, an MP for the Department of Transport. While they secretly celebrate successfully luring the humans into their plan, they are unaware of their conversation being witnessed by Harriet Jones, a backbench MP.When the Doctor returns to Rose, they are surrounded by soldiers, prompted by a call from Jackie to an Emergency Alien Hotline, and escorted to 10 Downing Street. The Doctor is asked to join a panel of alien experts, including those from UNIT, while Rose is escorted in the building by Harriet. Harriet explains the aliens to Rose, and together discover the corpse of the Prime Minister. They make to reveal their discovery but are caught by Blaine, who begins to unzip her human suit to attack them. Meanwhile, as the Doctor attempts to convince the experts of the forgery of the events, another human-disguised Slitheen sends an electrical shock through the assembled group, including the Doctor. These events lead to a cliffhanger, resolved in "World War Three"