The Government's terrorism watchdog has expressed concern about proposals to create a so-called "Big Brother" database holding details of every phone call, email and internet visit made in the UK.
Lord Carlile of Berriew, the independent reviewer of the counter-terrorism laws, described the "raw idea" of the database as awful and called for tight controls on its use.
His intervention, came as Home Secretary Jacqui Smith was expected to use a speech to set out her current thinking about the controversial scheme.
However, Lord Carlile told The Independent that the Government had an "unhappy" record when it came to safeguarding personal data. "As a raw idea it is awful," he said.
"However, it is a question of degrees and how it is developed. Searches should be made on a case-by-case basis with appropriate reviewing measures so that they can't be done willy-nilly by government."
It is reported that the database would hold all telephone numbers dialled and all addresses to which emails are sent, but not the details of conversations or the contents of emails.
Lord Carlile said that he would not want Britain to go as far as the Patriot Acts in the US where data searches cover anyone who has made contact with a terrorist suspect.
"There must be codes of practice... In counter-terrorism collation is everything but raw data only has a limited use," he said.
A Home Office spokesman said: "Changes to the way we communicate, due particularly to the internet revolution, will increasingly undermine our current capabilities to obtain communications data - essential for counter-terrorism and the investigation of crime - and use it to protect the public.
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"Losing the ability to use this data would have very serious consequences for law enforcement and intelligence gathering in the UK."
