The Creeper was a modified creeper plant created by the Biogenetic Research Centre by experimenting. The plant grows so fast that you can see it moving and is especially reactive against red light.
At the end of "The Demon Headmaster Strikes Again" the Creeper is used to test Eve's abilites and goes on to vapourize The Headmaster by lifting him onto the Evolution Accelerator supposedly 'killing' him for good.
The Creeper is shown briefly in "The Demon Headmaster Takes Over" as the Army reopen the centre to investigate and restore power as the Creeper is thought to have stopped growing. Claudia Rowe takes samples of the dead plant and the Army then supposedly burn all traces that is still in the BRC.