Britain's spy agencies will need a judge to sign off requests to hack into suspects' electronic devices or listen to their phone calls under a strengthened authorisation regime that will take effect within days.
The head of a watchdog set up to scrutinise the activities of MI5, MI6, GCHQ and law enforcement agencies told the Press Association the new approach represents a "seismic change".
In his first interview since being appointed Investigatory Powers Commissioner last year, Lord Justice Sir Adrian Fulford confirmed that his office would begin receiving warrants relating to the work of the intelligence services this month.
Under the "double lock" system introduced by the Investigatory Powers Act, requests to use the most intrusive techniques require approval from a judicial commissioner as well as a senior Government minister before they can take effect.
The process is being phased in, starting with warrants relating to equipment interference and targeted interception.
Equipment interference is the official term for operations where authorities interfere with electronic devices such as smartphones and PCs to obtain data as part of serious crime or national security investigations.
Agencies seek targeted interception warrants where they wish to access the content of a communication, such as listening to a phone call or reading an email or text message.
Requests to sweep up data in bulk will fall under the new regime from next month.
By the end of this year it is expected that the majority of investigatory powers and the hundreds of public bodies that use them will be subject to the Commissioner's oversight.
Sir Adrian highlighted the range of activity that now needs judicial approval and the creation of a single oversight body - there were previously three separate watchdogs - as key changes in the IP Act.
"That is a seismic change really in the way this country goes about this kind of work," he said.
Fifteen senior judges will weigh up warrants, with reserve commissioners on standby in case there is a sudden spike in requests.
Sir Adrian said: "The first warrants will start to come through under the Act this month and we are starting to increase the number of commissioners on duty at any one time to ensure we have got sufficient capacity to turn round the applications extremely quickly."
The Commissioner's office has "unfettered" access to agencies' records to ensure the powers are being used properly.
Sir Adrian said: "All of the indications I've had so far are that the security agencies and law enforcement take their responsibilities extremely seriously in this field."
The commissioner acknowledged that the new approach represents a "very considerable change" for the intelligence services.
"They are undoubtedly very keenly aware that there are going to be some sceptical and probing judges looking at all of the aspects of their work which relate to investigatory powers," he said.
"I think that has brought about not a change of culture, but it has made them focus in much greater detail than perhaps was the case before as to the justification that could be provided for everything that they do.
"We will be going in some real detail into the files and records of all of the bodies that have got investigatory powers to make sure they are not inappropriately hoovering up information."
No targets will be set for approvals or rejections of warrants.
"It doesn't matter whether there have been a lot of terrorist outrages or none, the commissioners will look at each application on its own merits, completely unaffected by what may or may not be a period of national emergency", Sir Adrian said.
"There isn't going to be any tendency either to grant or refuse."
He noted that by the time they reach commissioners' desks, warrants will have gone through many stages already.
"So if there's a high percentage of warrants being granted, I will not see that in any way as being an indicator that my office is not providing the kind of scrutiny that's required," he said.
Sir Adrian expressed confidence that provision to sanction the use of powers without prior judicial approval in emergency cases would not be misused, pointing out that warrants could still be revoked later.
"In addition, if I thought the provisions were being improperly used, it would not take me very long to raise this at the highest level with the head of whichever agency was responsible and if necessary with the Prime Minister," he said.
"I don't anticipate that this is going to happen."
Passed in November 2016, the IP Act was drawn up following controversy sparked by Edward Snowden's revelations about intelligence techniques.
Sir Adrian said: "We are now as a country I think in a much better place in terms of there being really full understanding of the extent of and the limits of the opportunities which the security services have to go into areas of our lives which ordinarily we would consider to be private and sacrosanct."