Sip Fel-Fotch Passameer-Day Slitheen is a member of the Slitheen a criminal family from Raxacoricofallapatorius and a minor antagonist in the Doctor Who episodes Aliens of London and World War Three.
He along with Jocrassa, Blon and several other members of the Passameer-Day branch of the family came to Earth in 2006 with plans to start World War Three which would turn Earth into molten slag which would then be sold as cheap fuel for spaceships. Whilst on Earth, Sip disguised himself as a police officer named Strickland and was sent out to kill Jackie Tyler but she was able to escape.
Later Sip appeared at the home of Mickey Smith and tried to kill both Jackie and Mickey there. Through as Sip was breaking through the front door Mickey contacted The Ninth Doctor who after discovering that the Slitheen come from Raxacoricofallapatorius, asks Mickey if he has got any vinegar which is deadly to the aliens as they are calcium based live forms. Jackie then pours all the food with vinegar in it into a jug which she then throws onto Sip and causes him to explode. Asquith Slitheen goes to Jocrassa to inform him of Sip's death, to which the latter says that he knew of the death as he felt it.
As Strickland, Sip is played by Steve Spiers and his Slitheen form is played by Paul Kasey.