Hillsborough 'surveillance' investigation possible - May
Claims that police put Hillsborough families under surveillance could form part of the investigations into the disaster, the Home Secretary has said.
Liverpool Walton Labour MP Steve Rotheram told the Commons families had been "shadowed like terrorists".
Theresa May said she could not compel police forces to "confirm or deny" any monitoring of families.
Police watchdog the IPCC has not received a formal complaint, she said, but would look into concerns.
The IPCC is conducting its biggest-ever investigation into the tragedy.
The Home Secretary told the Commons forces "could be ordered" to release all documents connected to the disaster if investigators encounter problems.
Addressing the undercover surveillance issue, she said: "No formal complaint or allegation has been made to the IPCC, but it is aware of the concerns and it is considering how it should best address those concerns.
"Of course, it is reviewing the material in relation to Hillsborough so if they discover any evidence in their investigation that suggests surveillance may have taken place of the sort that's been suggested, then they will of course pursue that evidence."
The IPCC previously said it was not actively pursuing allegations of spying on families and campaigners.
Mrs May said more than 250 new witnesses had come forward to give evidence to the inquiry into the deaths and the aftermath..
The IPCC has ordered an investigation into the police's handling of the tragedy in Sheffield, where 96 Liverpool football fans died in April 1989.
More than 2,500 police notebooks are also being studied for the first time after disputes over their accounts.
South Yorkshire Police said it had conducted a thorough search of the entire police estate.
"The searches led to the recovery of approximately 2,500 books dated between 1972 and 2007," a spokesman said. "Some officers provided numerous books spanning a number of years."
The majority of the pocket notebooks "have little or no relevance" to the disaster.
He added: "At all times we made it clear that the Hillsborough Independent Panel could have access to any documents they requested. We adhered to this offer throughout."
The spokesman said the force is "not suggesting or implying that there is a link between the blood alcohol levels of the deceased and the cause of the disaster".
Relatives of Liverpool fans killed in the Hillsborough disaster have previously called on the Metropolitan Police to answer claims officers spied on them.
Sheila Coleman, of the Hillsborough Justice Campaign, urged police to show "transparency" and admit spying.
Ninety-five victims were crushed to death in Britain's worst sporting disaster at Sheffield Wednesday's Hillsborough stadium during Liverpool's FA Cup semi-final against Nottingham Forest.
The 96th victim died in 1993 when the Law Lords ruled that doctors could stop feeding him.
As well as fresh inquests, there are two ongoing investigations into the disaster.
The IPCC is examining police actions during and after the tragedy, while former Durham Chief Constable Jon Stoddart is looking at the causes of the tragedy and the deaths, and examining the actions of a range of organisations and bodies, including South Yorkshire Police.
New inquests into the 96 deaths are due to begin in Warrington, Cheshire, on 31 March.