Mr Blair knows that bugging elected representatives will be fiercely opposed by many in Parliament but is confident he can argue the case over their heads that nothing - and no one - should be off-limits in the fight against terrorism. "Let no one be in any doubt," he declared in the wake of the London bombings, "the rule of the game are changing."
In truth, say critics, the rules have been changing ever since Mr Blair became PM and he has overseen a massive expansion of the state's capacity to spy on private individuals. There can be little doubt that, over the past eight years, technology and new legislation have significantly increased the security services' capacity to peer into our lives.
From the dramatic expansion of DNA and other databases to the multiple surveillance applications of satellite technology and new powers to read emails and texts, little now remains obscured from official snooping. Indeed, the Prime Minister recently boasted that he had "doubled the capacity" of MI5 in recent years.
Mr Blair has used the threat of international terrorism or crime to justify every reduction of civil liberty while pledging the safeguard of democratic oversight. Now even that oversight is under attack as the 40-year-old convention that MPs' communications should not be intercepted is to be torn up.
The history of how the Wilson Doctrine came into existence helps to explain why senior MPs and constitutional experts are so concerned at its imminent demise.
In late 1966, in the midst of the Cold War, Wilson had been forced on to the defensive after his extraordinary attack on the organisers of a seamen's strike, among whom was a young John Prescott. Challenged to justify his claim that the union was being manipulated by a "tightly knit group of politically motivated men", Wilson hinted at intelligence supplied by MI5.
It caused an uproar, and MPs demanded to know whether their phones were being tapped. On 17 November Wilson appeared in the Commons to give a statement that has been endorsed by every subsequent Prime Minister - until now. Wilson said there "should be no tapping whatsoever" of MPs' phones and that if it was considered necessary to change the policy, the Commons would be told.
Wilson said that he understood the "seriousness" of concerns, "particularly if tapping comes to be developed in this country on the scale on which it has developed in other countries". He could have little conception about the "scale" of interception technology 40 years on, nor how much the state could know about the lives of its citizens.
As detailed on this page, the scope for surveillance is increasing rapidly thanks to satellites, scanners, CCTV, information sharing and, shortly, ID cards. The legislative framework for this spying boom is laid out in the Regulation of Investigatory Powers Act (Ripa) 2000, which was supposed to reconcile new methods of snooping with human rights.
New watchdogs were created supposedly to ensure that the security services kept within the rules. But, ironically, Mr Blair says it is one of the new regulators who is pressing for the change to the Wilson Doctrine. In an almost unnoticed Commons statement last month, the PM said that Sir Swinton Thomas, the Interception of Communications Commissioner, had written to him saying that Ripa's "regulatory framework" had "possible implications" for the ban on tapping MPs' phones.
Most ministers and officials involved in the issue believe, however, that it is Mr Blair who is most keen to sweep away what he believes is a "Cold War anomaly".
The doctrine has come close to being breached on a number of previous occasions. Two years ago, for example, it emerged that it clearly does not extend to Sinn Fein's elected representatives.
Gerry Adams revealed that a listening device had been planted in a car used by him and other senior party figures. Eliza Manningham-Buller, head of MI5, was later reported to have privately admitted that the security services planted the bug. However, since Mr Adams refuses to swear an oath of allegiance to the Queen, he is not formally an MP - and is therefore considered fair game by the snoopers.
It is incidents like this that lead experts such as Peter Hennessy, professor of contemporary history at Queen Mary, University of London, to believe that the doctrine is scrupulously observed by the security services at all times. Nevertheless, he says he finds it "pretty odd" that the Government is preparing to dismantle it.
Only Mr Blair's sternest critics would suggest that he is motivated by anything other than a desire to give to the security services everything they say they need to tackle terrorism.
The problem, as seen by champions of Parliament such as Labour MP Andrew Mackinlay, is who is to watch the watchers. "Governments can never be trusted on their own not to confuse national interest with what is in their political interest," he says.
Additional reporting by Glen Kristensen and Sara Newman
Big Brother Blair and the war on terror
A fifth of the world's CCTV cameras are in the UK, and the average person is caught on film 300 times a day. Britain's four million cameras cover almost every town centre, and the numbers are growing. Each year, an estimated £300m is spent on CCTV. The London bombings demonstrated their advantages to spectacular effect, but Liberty wants clearer controls to ensure information is not misused.
In 1997, there were 1,712 warrants allowing phone taps. In 2003, there were 4,827, about two and a half times the total when Labour came to power. The increase is more stark given that the rules have changed so warrants are issued against individuals, not communication providers, such as BT. Investigators used to need separate warrants. Now the Home Secretary need sign just one to intercept all communications.
More than 5 per cent of the UK population - about three million people - are registered on one of the world's largest DNA data-bases. Anyone arrested can be sampled and permanently entered into the National DNA Database. Prosecution is not a condition for inclusion. About 140,000 people on it have not been charged or cautioned for an offence. Some 37 per cent of black males are on the register, and 9 per cent of white men.
SPIES IN THE SKY
Trials have started in Yorkshire of "tag-and-beacon" road pricing technology. Similar trials are to be held in London soon, possibly to replace the system for the congestion charge. But the real surveillance advance will come with satellite road pricing. Fitting tracking devices in cars to replace road tax with variable charges will also help the security services pinpoint details of every road journey made in Britain.
ID cards are scheduled to come into use in 2008, subject to parliamentary approval. More than 50 pieces of information relating to the holder, including biometric information (iris patterns, fingerprints), will be on the cards. The Government says they will be invaluable in the fight against terrorism, organised crime and benefit fraud. Checks against a compulsory identity register are to be offered to private firms.
SPIES ON THE NET
The Regulation of Investigatory Powers Act 2000 gave police and security services powers to monitor websites and intercept emails. The legislation provides for heavy penalties for failing to surrender passwords or encryption keys. Internet service providers are responsible for the installation of remote-controlled black boxes that relay all data passing through their computers to MI5.
Details of every car numberplate, including date, time and location, are to be stored for at least two years, whether the owner has committed an offence or not. A control centre, which opens in April, can process and track 50 million plates a day. Plans are in place to enable 100 million a day, with records stored for five years. Commuters using London's Oystercard are providing a detailed record of their movements each day.
A millimetre wave machine, or "body scanner", is being tested on Heathrow Express commuters at Paddington. The scanner, a 7m-long steel box, creates a virtual image of people inside. An operator views this on a screen and can see any concealed objects. Critics say, aside from privacy, the health and safety aspects of such devices are unknown, because the technology is similar to that used on mobile phone masts.
Details on England's 11 million children are to go on an electronic database along with information on their families. Teachers, social workers and others working with children can access it. Set-up costs are estimated at £224m, and annual running costs £41m. Critics say the index will capture information on almost every child, except those most likely to be at risk. Trials suggest even schools have several addresses for some children.
The NHS is compiling a database of medical history on all patients. Inclusion is not compulsory, but patients must actively opt out or it will be assumed they have opted in. The records would allow huge improvements in patient care, but the NHS is under pressure to allow the security services access to private medical data. It is believed MI5 has already asked to view the database.