Police are investigating an alleged break-in at the offices of Labour leader Ed Miliband in the Houses of Parliament.
Scotland Yard received a report shortly before 7pm on Friday of a forced entry to the premises in the Norman Shaw buildings.
"Police were contacted at 6.55pm regarding an alleged forced entry to an office in the Palace of Westminster. Inquiries continue," a spokesman said.
It is understood a member of the Opposition leader's staff found a door had been forced but it is unclear whether anything was missing from the room.
A senior Labour source said: "We don't know if anything was taken, and we don't know the motivation for this crime.
"But we are deeply concerned that this can take place within the Palace of Westminster."
Sky News' political correspondent Peter Spencer said: "We understand there has been a spate of laptop thefts recently.
"How much information could be contained on a laptop and why would anyone want it?
"It could be nothing but one thinks of the Watergate investigation and that brought down a president."
Mr Miliband was away from Westminster at the time of the alleged break-in having attended a Labour party conference event in the Midlands.