The Independent Police Complaints Commission (IPCC) could formally investigate the role played by Britain's most senior police officer, Sir Bernard Hogan-Howe, in the Hillsborough disaster.
It said it had received a complaint about Metropolitan police commissioner Hogan-Howe, who was on duty at Sheffield Boys' Club where families waited for news of loved ones on the day 96 Liverpool football fans were killed in 1989.
The IPCC is looking at the treatment of relatives in the immediate aftermath of the disaster and how officers managed the task of informing them.
The watchdog contacted the family of 14-year-old victim Adam Spearritt, following reports his name was wrongly read out on a list of people believed to alive by an unidentified police officer at the club.
In a statement, the IPCC confirmed it had received a complaint about Sir Bernard - an inspector at South Yorkshire Police at the time of the Hillsborough disaster - which had been passed to the Mayor's Office for Policing and Crime.
"The Independent Police Complaints Commission can confirm it has received a complaint about Sir Bernard Hogan-Howe in relation to his role at Hillsborough," it said.
"This complaint has been passed onto the Mayor's Office for Policing and Crime (MOPC) for recording as required by the complaints process.
"The MOPC is responsible for deciding whether complaints against the commissioner should be recorded and whether they should be referred to the IPCC. However in this instance the IPCC expects the matter to be recorded and referred."
A Met Police spokesman said: "As has been made clear, the commissioner will co-operate fully with any inquiries from the IPCC."
Fresh inquests into the deaths of the Hillsborough victims who died during or after the 1989 FA Cup semi-final are due to start in Warrington on March 31.
The disaster took place at Sheffield Wednesday's Hillsborough stadium on 15 April 1989 when fans were crushed to death at the match between Liverpool and Nottingham Forest.
The original inquest verdicts of accidental death were quashed in December, three months after the damning findings of Hillsborough Independent Panel report were released.
The watchdog has also written to former prime minister Sir John Major after he apologised to Hillsborough families for failing to order an inquiry when he was in power.
The ex-Tory leader claimed in a speech last month that police had ''pretty strong views'' that there was no need for a report into the disaster.
The IPCC said it has written to Sir John to establish further details and determine whether it should be incorporated into its inquiry.
The watchdog added: "At this stage we are investigating the processes and if, through that work, we identify individuals whose actions should be formally investigated then we will pursue that."
A spokesman for Sir John said he was unavailable for comment but confirmed his office had not yet received a letter from the IPCC.
More than 2,000 police notebooks have been located after a search of archive storerooms and 118 have been handed in by South Yorkshire Police officers who were on duty at Hillsborough, the IPCC said.
A witness appeal had prompted responses from 1,500 people and generated more than 750 lines of inquiry for investigators.
After interviews with serving and retired police officers, the IPCC said the number of police accounts of the day which had been amended stood at 240, up from the 164 originally identified by the Hillsborough Independent Panel.
It said 101 interviews had been carried out with officers.
Of the nine Hillsborough officers who declined to be interviewed, none are senior or suspected of criminal offences, the IPCC said.
Last year a damning report by the Hillsborough Independent Panel found that South Yorkshire Police orchestrated a cover-up, falsified documents and blamed innocent supporters in the aftermath.
The lives of 41 fans could have been saved, the report concluded, as it cleared supporters of any wrongdoing or blame for the disaster.