- Video report by ITV News correspondent Olivia Kinsley
Parliament has been hit by a cyber-security attack in which hackers have tried to access email accounts.
MPs and Lords have been left unable to access their emails remotely as a result of measures taken to stave off the attack.
Tory MP Andrew Bridgen suggested an attack like this could "absolutely" leave some people open to blackmail.
He said it was understandable that "constituents want to know the information they send to us is completely secure."
A House of Commons spokeswoman said they had on Friday "discovered unauthorised attempts to access parliamentary user accounts".
She said that remote access to emails had been disabled as part of work to stave off the attack.
Liam Fox, the Secretary of State for Trade, said it was "not at all surprising" to see efforts to hack into Parliamentary emails and that there had been repeated similar attempts in the past.
An email sent by parliamentary authorities to those impacted by the attack said that the alarm was raised after "unusual activity" was spotted.
"Closer investigation by our team confirmed that hackers were carrying out a sustained and determined attack on all parliamentary user accounts in an attempt to identify weak passwords," it added.
A number of MPs and Peers had posted on Twitter to say they could not access emails as a result of a cyber attack.
The attack follows reports that passwords for MPs and officials were being sold online by hackers.
A House of Commons spokeswoman said: "We have discovered unauthorised attempts to access accounts of parliamentary networks users and are investigating this ongoing incident, working closely with the National Cyber Security Centre.
Parliament has robust measures in place to protect all of our accounts and systems, and we are taking the necessary steps to protect and secure our network."
She added that officials had taken the decision to "temporarily" restrict remote access to emails "as a precaution".
The National Crime Agency said it was working with the NCSC on the issue.
Labour leader Jeremy Corbyn called for more investment in protection against hacking attacks.
"I think it indicates just how vulnerable we are to cyber attacks and our cyber security," he said of the cyber attack on Parliament.