Government terror watchdog Lord Carlile has expressed concern about the government's plan to build a giant database to store details of all citizens' phone calls, e-mails and internet use.
Lord Carlile told The Independent newspaper that the "raw idea" was "awful". He called for tight controls on its use.
The Liberal Democrat peer warned that it "should not be open season" for collecting data as part of the effort in fighting terrorism.
The controversial communications data collection scheme came to light earlier this year, and is expected to be included in a new Communications Data Bill introduced in the Queen's Speech next month.
The data collected would not include the content of phone conversations or messages sent, but would include dialled phone numbers, details of websites visited and e-mail addresses that had been sent messages.
Lord Carlile said the government had an "unhappy" record when it came to safeguarding personal data.
The Information Commissioner has already expressed concern about the planned database, saying it poses data protection risks.