Commissioner Cressida Dick says initial interviews and examination of evidence likely to take officers more than 12 months

The criminal investigation into the Grenfell Tower fire, which killed 71 people, is unlikely to be completed until 2019 at the earliest and could take years, the head of the Metropolitan police has said.

Scotland Yard has previously said individual and corporate manslaughter charges were being considered, but the Met commissioner, Cressida Dick, said on Wednesday that detectives were a long way from passing files to the Crown Prosecution Service and that she had asked for extra government funding over several years to help cover the costs of the inquiry.

Giving an update to the London Assembly, she said: “I think we will be looking at the best part of next year before we finish all the kind of reconstruction and forensic examination and, as you know, there are a very, very, very large number of people and records to either take statements from or examine forensically so I’m not going to put a timescale on that.”

She added: “I would be astonished if we were finishing the criminal investigation within 12 months, I am sure that it will be much more than that.”

Dick said about 200 detectives were working on the investigation, with 400 having been involved at its peak, and specialists from as far away as New York had been consulted.

The force has drawn up a list of 2,400 people to speak to, including members of the emergency services and residents.

More than 1,000 statements had already been taken and 2,500 exhibits seized, many from within the tower, and police needed to contact 336 organisations, including those involved in building, maintenance and management of the tower. Dick said that as far as she was aware, no one had been interviewed under caution so far.

The commissioner said specialist officers had recently completed a room-by-room fingertip search of the tower, sifting 15.5 tonnes of debris.

After a year in which there had been three terrorist attacks in the capital, Dick assured the assembly members that the Met was able to cope but said it had requested extra funds from the Home Office.

“We are cautiously hopeful that we will be able to make applications for this year in relation to the special grant that can be made available from the government in relation to both the terrorist attacks and Grenfell,” Dick told assembly members. “And I have made it clear that this is an investigation which will go on into future years and that therefore that needs to be factored in as well.”

Lawyers representing survivors and relatives of the victims began giving evidence to the public inquiry into the tragedy on Monday, amid anger among many that their voices were not being granted sufficient importance in the process.

Dick said she would not provide a “ticker tape update on who we’ve spoken to about what, when”, but added: “I believe that, in very difficult circumstances, we are keeping those who have been bereaved and indeed those who were residents and who have survived, as well informed as we reasonably can.”