A senior clerk at the House of Commons has denied using his work computer to download child pornography.
A senior clerk has denied 12 counts of making indecent images
Phillip Lyon is accused of visiting child porn sites almost daily.
The 38-year-old from Stanford le Hope, Essex, is also accused with collecting more than 1,000 images of children on his home computer.
Riel Karmy-Jones, prosecuting, told Southwark Crown Court Mr Lyon was discovered when an IT consultant opened a file showing "something terribly wrong".
The prosecution alleges Mr Lyon used his computer "to pursue his interest and perhaps curiosity in
this type of material".
"He searched for it on the internet and when found, downloaded it for his delectation later," Miss Karmy-Jones said.
Mr Lyon has denied 12 counts of making an indecent image of a child.
The allegations are said to have taken place between October 2001 and April 2002.
The prosecution claims Mr Lyon had far wider usage of the internet than the 12 charges before the court.
When arrested, the defendant allegedly compared his problem to that of a drug addict.
He allegedly told officers: "It is like a drug, you try one and you want to try something harder and it has a snowball effect."
Mr Lyon worked as a senior office clerk in the Upper Table Office at the Commons.
He researched Parliamentary questions to ensure they had not been asked on a previous occasion.
The case continues.