If 2011 was the year when the words "Operation Weeting" entered the popular lexicon, 2012 is likely to see "Operation Tuleta" added to the list of game-changing police investigations everybody is talking about.

Since it was set up six months ago, Scotland Yard's inquiry into allegations that private detectives were hired by newspapers to target computers of public figures has been overshadowed by Operation Weeting, which deals with the News of the World phone-hacking scandal.

But revelations that police are investigating evidence that emails sent and received by a Chancellor of the Exchequer were illegally accessed – making Gordon Brown the second Labour cabinet minister after Peter Hain to be potentially computer hacked – shows the significance that Tuleta is rapidly gaining.

It also shows how big the next headache to face the Metropolitan Police – and Britain's battered newspaper industry – is turning out to be. Among the cognoscenti of the phone-hacking scandal, there has long been a whisper that Tuleta could show wrongdoing on a scale similar – or greater than – the eavesdropping of voicemails on behalf of the NOTW. Scotland Yard said last month it thought there were about 800 victims of phone hacking. Weeting has 120 detectives and staff. Tuleta is examining nearly 20 computers containing 750,000 documents with a staff of eight officers.

It is also understood that while Weeting is restricted to the activities of a single (shut) newspaper, the computer hacking investigation is looking at the commissioning of private investigators by journalists on several titles.