The same law, contained in Part III of the Police Bill, which completed its Lords Committee Stage last night, will allow a similar sort of activity at the home of a journalist whose contacts might be useful to the police. And because the law will cover "conduct by a large number of persons in pursuit of a common purpose", it will legalise, to coin "Spycatcher" Peter Wright's memorable phrase, "bugging and burgling" at the home of an environmental protestor.
Extreme examples perhaps, but they will happen and we may never find out. Officers will get their authorisation from their chief constable or an assistant chief constable, or in the case of customs, a designated senior officer. That contrasts with the requirement for a warrant from a court, in the majority of cases, to search openly and seize property, and with the power to tap two-way telephone conversations, which, following a ruling by the European Court of Human Rights, needs a warrant from the Home Secretary under the 1985 Interception of Communications Act.
The go-ahead will be based on the chief officer's subjective assessment that the surveillance is likely to be of substantial value in the prevention or detection of serious crime, and can allow covert searching and/or bugging, or both.
People whose privacy, correspondence, home or office (including the office of their employers - a City institution, perhaps? - or indeed any other premises) is invaded do not have to be under suspicion of being disposed to commit serious crime themselves. And in another departure from the somewhat different standards in the Interception of Communications Act, all material or information garnered - even where the new Commissioner proposed by the Bill to handle complaints finds it not properly authorised - will be admissible as evidence in a trial.
The Government took its cue for that provision from a law lords' ruling in July. This stated that evidence obtained through trespass and bugging (under the existing Home Office guidelines that the Act is to replace) could be used in a prosecution, which otherwise would not have gone ahead, against a drugs importer. It is tucked away in a schedule, as is an instruction to the Commissioner not to give any reasons for rejecting a complaint.
The Commissioner will be a senior serving or retired judge, but he or she will have a highly limited remit to overturn an authorisation in the face of a complaint. A chief constable will be able to authorise the surveillance or covert search if he or she thinks it necessary. That means that the Commissioner can only interfere if the decision, in legal jargon, is so unreasonable as to be "perverse".
The Bill leaves nothing to chance by specifying that judicial review principles should be applied. The Commissioner's decisions, for good measure, cannot be "appealed or questioned in any court." In short, the powers in the Bill could not have been drafted more widely. The prospects of getting them drawn more tightly are slim.
Of course, the aim of this substantial increase of virtually self-regulatory police powers is detecting and catching serious criminals, as Baroness Blatch, the Home Office minister presently handling the Bill, emphasised in a recent letter to Lord Browne-Wilkinson, a law lord. He is one of a handful who have dared to put their heads above the parapet to invoke the constitutional principle that ministers, officials or police officers are supposed to have no greater right than any ordinary citizen to invade an Englishman's home, and suggest that the powers in the Bill are too wide.
"One could argue that it is crime that poses the biggest threat," wrote the baroness. "Our homes are, of course, much more likely to be violated by burglars than the executive. However, the provisions are not meant to tackle this sort of criminal, or the protestor against a new road or the journalist who refuses to reveal his source. Our provisions are needed to tackle the serious organised criminal ... who may infiltrate our banking and financial institutions and who has no qualms about using legitimate fronts, such as firms of solicitors or accountants, to launder the vast profits from drug trafficking and other illicit activities."
She invoked another recent legal case to support the Government's insistence that the courts should not be involved, where a judge had said it would be impossible to put himself in a chief constable's shoes to make an operational decision to authorise or not. Warranting by the Home Secretary, the authorisation procedure for MI5 - the first inroad into the "Englishman's home" principle - could be seen as interfering with police independence.
So the message is "trust the police", and it is one that Labour is prepared, in the final event, to sign up to. Lord McIntosh, the party's home affairs spokesman in the Lords, made a so far unsuccessful attempt last week to introduce a narrowly-drawn amendment to protect legal privilege, but not currently protected documents such as personal records or journalistic and other confidential material for which a court order must be sought.
In truth, nobody who has studied the progress of this part of the Bill expects it to be changed very much at all when it emerges from the Lords to complete an equally uneventful passage through the Commons.
Labour has convinced itself, if not its critics, that despite the blanket nature of the Bill, the powers will be used sparingly and responsibly under authority given at a very senior level by chief constables, who are not going to want to be the target of challenges, however ineffectual, from aggrieved citizens.
Despite the fact that the tribunals set up to regulate MI5, MI6 and GCHQ have never upheld a single complaint, it is prepared to have faith in the Commissioner. But three leading barristers have drawn up an opinion for Liberty, the civil rights organisation, saying that the power to be vested in chief officers will violate Article 8 of the European Convention on Human Rights which guarantees respect for privacy, home and correspondence, and Article 13, which provides for the right to effective legal remedy.
This is the same human rights convention that Labour has pledged to make part of British law. Under a Tory government, Labour is in a cleft stick over law and order. But the political embarrassment will catch up with a Labour party in government when the first human rights complaint after a bungled police operation is launched. And in years to come, when suspicions may abound - for who will ever know for sure? - that covert searches and snooping have become routine, ministers can reflect on the fact that it all began here.