Steve: This is a sofa. It is designed by clever scientists in such a way so is to shield the unprotected user from the risk of skin-abrasions, serious headtrauma and, of course, (Steve ducks behind the sofa) Daleks.
This is an allusion to the long-lived sci-fi-series "Doctor Who" in which the Daleks, a semi-robotic alien lifeform, are one of the arch-enemies. This series is so scary at times that most children only watch it from behind the sofa, hence Steves reference to the sofa granting protection from Daleks.
In the UK this is such a well known fact that an exhibition on the series was even called "Behind The Sofa".
In 2010, Coupling's creator and writer Steven Moffat took over as head writer and show runner for "Doctor Who."