David Cameron insisted there were "significant gaps" in UK security as he defended Government plans to allow all calls, emails, texts and website visits to be monitored.
The Prime Minister said his job was to do "everything that is necessary" to keep the country safe.
Mr Cameron said the coalition would "respect" civil liberties but wanted to "plug the gap" in defences.
Liberal Democrat president Tim Farron vows the party would "kill" proposals for increased monitoring of emails and internet use.
Ministers are preparing a major expansion of powers to monitor the email exchanges and website visits of every person in the UK.