Martin Hickman: These claims cannot be brushed under the carpet

A murky scandal has just become much darker. The suggestion that a private investigator targeted a serving prime minister, the governor of the Bank of England and the commissioner of the Metropolitan Police is, in itself, astonishing.

What pours petrol on the flames is the suggestion that Scotland Yard is not investigating – despite apparently having a tranche of incriminating paperwork. The question is: why? Already, the Yard has been scolded for failing to mount a proper investigation into Glenn Mulcaire, the News of the World's exclusively contracted private eye who hacked into the voicemails of Prince William and hundreds of other public figures.

It could be resources: 45 detectives are working on Operation Weeting into Mulcaire, more than a major murder inquiry. Or it could be incompetence: that the Yard does not appreciate that allegations that a private detective and his network of dirty diggers were snooping on the men running the country, the economy, and the police, are serious.

More plausibly, it could be embarrassment. Embarrassment that, just as it failed to investigate Mulcaire amid suspicions that senior officers enjoyed an unhealthily close relationship with the NOTW, the Yard has failed again to investigate evidence about Rupert Murdoch's empire which it has under its own nose.

Whichever is true, the Met will come under intense political pressure to widen Sue Akers' inquiry, just as it was forced by the drip-drip of disclosure in the civil phone hacking cases to launch Weeting.

The true importance of these new allegations, though, is that they suggest the "dark arts" of information-gathering were not being carried out by just one prolific individual, but two.

And it is just possible that the huge fuss surrounding Mulcaire's snooping may yet be eclipsed by an even more sinister attempt to target the private lives of the country's political leaders. This scandal is only half-way through.