Democrat oversight of the nation’s intelligence services “barely exists”, MP Tom Watson has warned.
And he said the security services may have breached the human rights of British citizens - by secretly watching how they used the internet.
The Black Country MP was speaking in the House of Commons following reports that the British Government Communications Headquarters (GCHQ) in Cheltenham is monitoring data sent using the internet and sharing the information with the US National Security Agency (NSA).
Papers leaked to The Guardian by US computer specialist Edward Snowden, a former CIA employee and NSA contractor, apparently show that GCHQ has placed probes on fibre optic cables used to transmit data to and from the UK.
This would include many emails and other forms of communication sent between UK citizens, as the way the internet works means that their data might in many cases be sent to servers in other countries and then come back into the UK.
The surveillance programme, called Tempora, has been running since 2011.
Mr Watson (Lab West Bromwich East), who has previously spoken out on issues including phone hacking by parts of the newspaper industry, said revelations about the extent of internet surveillance by the security services had led to widespread debate in the US, but were largely ignored in the UK.
He said: “ We have avoided discussing this matter in all but whispered tones, while the legislatures of the US, Brazil and Europe have been rocked by the Snowden revelations. Yet in the UK, the main parties have paid scant attention to the issue.
“The problem is this: the GCHQ Tempora programme has been mining our internet communications data without public knowledge on a colossal scale.
“There has been little public and parliamentary debate about whether that conforms to article 8 of the European convention on human rights, which protects the right to private and family life and correspondence.”
There had been no debate about whether Tempora was authorised by any legislation, he added.
Mr Watson said telecoms businesses appeared to have co-operated with the security services to allow probes to be fitted to cables - but asked Ministers to reveal whether they had done so voluntarily.
He said: “The security services have clearly made the trade-off that the intelligence obtained is worth the invasion of privacy.
“They are judged on the quality of the intelligence they obtain and little else. Of course they are going to make that trade-off 100 per cent of the time.
“I want to know whether the telecoms companies have voluntarily entered into that agreement, or whether they have been obliged to do so under UK or US law.”
The security services are overseen on behalf of Parliament by the Intelligence and Security Committee, which includes nine MPs and peers and is chaired by former Foreign Secretary Sir Malcolm Rifkind.
But speaking after the debate, Mr Watson said: “Its remit is so broad that it is difficult to see how one committee can hold all of these agencies, departments and units to account effectively.”
He added: “Oversight needs to understand what is being asked of us, it needs technical competence, and the public needs to trust it. But the current set up has failed to show it has any of these qualities.
“Parliamentary scrutiny hasn’t just failed. It barely exists.”
Speaking in the same debate, Walsall MP David Winnick (Lab Walsall North) praised The Guardian and Mr Snowden for revealing the surveillance. It followed comments by the Prime Minster who claimed last month that the leaks had helped people “who want to do us harm”.
Mr Winnick said: “It is absolutely essential that the information that Snowden has revealed, which is not helping the terrorists, but which we should know about it - really, to a large extent, it was done in our name - should be in the public domain, and I am glad that it is.”
Home Office Minister James Brokenshire said: “The work of the security and intelligence agencies is carried out in accordance with a strict legal and policy framework, which ensures that their activities are authorised, necessary and proportionate, and that there is rigorous oversight, including from Secretaries of State, from the interception of communications commissioner and the intelligence services commissioner, as well as from the Intelligence and Security Committee, itself.”
He added: “Oversight is absolutely essential, but much of it must necessarily take place behind closed doors to ensure that secret intelligence remains secret.
“That has to be a key theme in the work undertaken, because although I recognise the desire for transparency, at the same time there has to be a role for secrets in order for our agencies to conduct the work that they do.”