British Prime Minister David Cameron is facing a growing backlash from within his own party over plans to extend the government's powers to monitor people's email exchanges and website visits.

The measures would see Internet firms being instructed to install hardware enabling GCHQ -- the government's electronic "listening" agency -- to examine "on demand" and in "real time" details of any phone call, text message or email, and any website visited.

A previous bid to introduce a similar law was dropped by Labour in 2006 amid fierce opposition from the Conservatives and the Liberal Democrats.

The Home Office interior ministry argues the proposals, expected to be unveiled in next month's Queen's Speech, are "vital" to combat terrorism and organised crime.

It also stressed a warrant would be needed to access the content of the communications being monitored.

However, data showing the time, duration and phone numbers in a communication or email addresses could be accessed without a warrant.

The latest government plans have been opposed by rights groups and now a growing number of Tory MPs.

"It is not focusing on terrorists or on criminals. It is absolutely everybody. Historically governments have been kept out of our private lives," Conservative former shadow interior minister David Davis told BBC radio.

"Our freedom and privacy has been protected by using the courts by saying 'If you want to intercept, if you want to look at something, fine, if it is a terrorist or a criminal go and ask a magistrate and you'll get your approval'.

"You shouldn't go beyond that in a decent, civilised society but that is what is being proposed."

Mark Field, a Conservative member of the the parliamentary Intelligence and Security Committee, which oversees the work of the intelligence agencies, raised the likelihood of significant opposition from MPs over the measures.

"I would imagine... that they would be extremely concerned if this were to see the light of day in legislation in this entirely unvarnished way," he told BBC radio.

"I think the notion of having a warrant and having this done through an open and transparent legal process is one that has worked well and I hope that it will work well in the future."

Shami Chakrabarti, director of civil liberties group Liberty, denounced the move as "a pretty drastic step in a democracy."

The Home Office said ministers were preparing to legislate "as soon as parliamentary time allows" but said the data to be monitored would not include content.

"It is vital that police and security services are able to obtain communications data in certain circumstances to investigate serious crime and terrorism and to protect the public," a spokesman said.

"We need to take action to maintain the continued availability of communications data as technology changes.

"Communications data includes time, duration and dialling numbers of a phone call, or an email address.

"It does not include the content of any phone call or email and it is not the intention of government to make changes to the existing legal basis for the interception of communications."