Lord Steyn, one of the country's most senior judges until he retired from the House of Lords last month, accused the Prime Minister of mounting measures to tackle terrorism that will fall foul of human rights laws.
In an interview with The Independent, he added that locking up terror suspects for three months would also bring about miscarriages of justice. Lord Steyn, who only now is able to make public his thoughts on government policy, describes the extended detention proposal as "exorbitant and unnecessary" and may breach the European Convention on Human Rights.
His comments follow reservations expressed by Lord Goldsmith, the Attorney General.
He has reportedly told the Home Secretary, Charles Clarke, that he is not convinced that it would be right to detain terror suspects for 90 days.
Yesterday a spokeswoman for the Attorney General told The Independent that Lord Goldsmith did not believe that the case for 90- day detentions had been made, but could see an argument for increasing it beyond the current 14 days.
"If it is increased he wants there to be rigorous judicial scrutiny." she said.
In his wide-ranging interview, Lord Steyn also warns the Government that ministers must respect the independence of the judiciary, and criticises Mr Blair for saying in his Labour Party conference speech that the rules of the game had changed since the 7 July bombings in London.
He says: "Perhaps Mr Blair should know that when he talks about the rules of the game he should know this is not a game, this is a deathly serious and earnest matter and that what we [the judges] do apply is the law."
This week the Home Affairs select committee will hear evidence on the impact of the anti-terror proposals ahead of the publication of more detail of the measures.
The government has already abandoned its plans to make it an offence to glorify terrorist acts after it was shown that praise of civil rights protestors such as Nelson Mandela could be caught by the legislation. Lord Steyn, a South African-born judge, is equally scathing about Labour's refusal to use intercept evidence in court against suspects.
"I have never been able to accept that intercept can't be used in court. In the modern age it is very valuable evidence, very, very compelling, frequently possible to use it, so why not use it." He argues: "The say-so of the security services is not enough ... we must evaluate things directly. [intercept evidence] ... will lead to convictions."
Lord Steyn, who has served the bench for 20 years, 10 of those in the House of Lords, is also concerned about plans to bring in a national ID card.
"I'm not in principle against it if its advantages can be shown to be demonstrable but I have great, great reservations about the practicality of it ... and I am deeply sceptical."
The former law lord also takes issue with the Government over the religious hatred bill which will make it a criminal offence to incite hatred of a religious group.
"It will undoubtedly amount to a serious restriction on liberty of expression. I think the bill goes much too far. All sorts of very trivial matters will be caught by this, really trivial matters of jokes and satire."Reuse content