It appears "possible that some people may have committed offences" Scotland Yard's head of counter-terrorism told MPs when she updated them on the state of the investigation into the material seized from David Miranda in August.

Assistant commissioner Cressida Dick also said that the Metropolitan police were looking at the "potential" that terrorism offences had been committed involving communicating information about members of the intelligence services.

Dick was responding to questions form the Commons home affairs select committee about whether there was an active police investigation into the Guardian over the disclosure of the GCHQ/NSA mass snooping documents.

Earlier Alan Rusbridger, the Guardian editor, had told MPs he did not know whether or not there was active Met investigation into the Guardian and he had not received "any knock on the door" so far.

Dick said that the police were continuing with their examination of the "large amount of material" which was seized from Miranda, who is the partner of the former Guardian journalist, Glenn Greenwald, when he was stopped at Heathrow airport in August. Dick confirmed that the material was being examined to see if Official Secrets Act or terrorism offences had been committed.

"We are continuing with that inquiry. We are taking that carefully. There is a lot of difficult material to find our way into. We will go where the evidence takes us. We will be proportionate and careful about every step we take," she said.

"It appears possible that some people may have committed offences. We need to establish whether they have or haven't. That involves scoping a huge amount of material."

She confirmed that the police would take "very seriously" any complaints about other offences by others or by parties apparently involved or not involved in the case.

In response to a question from the Conservative MP, Mark Reckless, as to whether they were also looking at possible offences under section 58a of the Terrorism Act 2000, which covers the communication of information about members of the intelligence services, Dick replied: "Yes indeed, we are looking at that potential."

Bernard Hogan-Howe, the Met commissioner, clarified in response to MPs questions that investigation was not the result of a complaint but stemmed from the material seized when Miranda was stopped at Heathrow under schedule 7 of the Terrorism 2000 Act. He said they were waiting the outcome of the judicial review into the legality of the seizure of that material.

Dick confirmed that if the police believed there was sufficient evidence to prosecute in the case, the Crown Prosecution Service would consider the file and then the attorney-general might possibly be involved in a decision to prosecute.