Parliament has been hit by a cyber security attack.
MPs and Peers have been left unable to remotely access their emails as a result of the incident, Parliamentary authorities said.
A House of Commons spokeswoman said: "The Houses of Parliament have discovered unauthorised attempts to access parliamentary user accounts.
"We are continuing to investigate this incident and take further measures to secure the computer network, liaising with the National Cyber Security Centre.
"We have systems in place to protect member and staff accounts and are taking the necessary steps to protect our systems."
The spokeswoman said that the lack of remote access for users was not part of the attack, but due to protection measures dealing with the incident.
She said: "Parliament has disabled remote access to protect the network."
Liberal Democrat peer Baron Rennard tweeted: "Cyber security attack on Westminster, Parliamentary e.mails may not work remotely."
The attack follows reports that passwords for MPs and officials were being sold online by hackers.
Henry Smith, Tory MP for Crawley, tweeted: "Sorry no parliamentary email access today - we're under cyber attack from Kim Jong Un, (Vladimir) Putin or a kid in his mom's basement or something..."
The National Crime Agency said it was working with the NCSC on the issue.
It tweeted: "We're aware of a possible cyber incident affecting parliament & are actively cooperating with @ncsc who're leading the operational response."