David Cameron wants a fresh push after the next election to "modernise" laws to allow monitoring of people's online activity, after admitting there was little chance of progress before then.

The prime minister told a parliamentary committee that gathering communications data was "politically contentious" but vital to keep citizens safe.

He said TV crime dramas illustrated the value of monitoring mobile data.

A communications data bill was dropped last year after Lib Dem objections.

The idea of the bill was to allow government access to details of who called whom, when and where - although ministers said it would not cover the content of calls.

It would also have extended laws to cover new online forms of communication, such as internet-based phone services like Skype, and there were suggestions it could also give intelligence services real-time access to the data.

'Raised questions'

Critics called it a "snooper's charter", as they had when the previous Labour government floated a similar plan. Lib Dem leader Nick Clegg, who had initially backed the idea of a bill, said the finalised proposals "went too far".

The subsequent Edward Snowden revelations about the data being gathered secretly by US and UK intelligence services led to the proposed bill dropping down the agenda.

Mr Cameron told the cross-party Joint Committee on the National Security Strategy he did not think the public reaction to Snowden's revelations about secret US data surveillance programmes had been the same as the media reaction.

He said it had "raised questions about who has access to my data and why".

But, added the prime minister, the "sense" he had was that British public's attitude to the revelations was that they showed the intelligence services were doing their job of keeping people safe.

He said: "Over time we are going to have to modernise the legislative framework and practice when it comes to dealing with communications data.

"It's obviously politically quite a contentious topic. I'm not sure we'll make progress on it in the coming months in terms of legislation - there may be some things short of legislation which we can do."

He said politicians, police chiefs, the intelligence services all had to explain why changes were needed.

Image copyright Reuters Image caption Edward Snowden currently lives in Russia

"In the most serious crimes [such as] child abduction communications data... is absolutely vital. I love watching, as I probably should stop telling people, crime dramas on the television. There's hardly a crime drama where a crime is solved without using the data of a mobile communications device."

"What we have to explain to people is that... if we don't modernise the practice and the law, over time we will have the communications data to solve these horrible crimes on a shrinking proportion of the total use of devices and that is a real problem for keeping people safe.

"We have got to make this explanation very clearly, really get it out to people and then build, perhaps at the start of the next Parliament, a cross party case for sensible legislation to deal with this issue.

"I think it is possible, but I think it is going to take a lot of work by politicians across parties to try to take the civil liberties concerns seriously, but get them in proportion so we can make some progress."

Emma Carr, deputy director of Big Brother Watch, said: "It is clear that the public have no idea about the true scale of surveillance already going on and that's why the entire legal framework for surveillance needs reviewing and reforming wholesale.

"If the prime minister wants to update the law, this is absolutely necessary and we would welcome the opportunity to have that debate."