Lawyers in the Guildford pub bombing inquest have threatened Surrey Police with High Court action over archives removed from a history centre.
The Surrey History Centre records were deposited by ex Ch Supt Bob Bartlett.
A memo seen by the BBC said police "seized" files and one "will be destroyed" while others were required to be destroyed after seven years.
KRW Law have sought urgent confirmation the files still exist. Surrey Police said no files had been destroyed.
The memo given to the BBC, and reported at the weekend, said police "entered the Surrey History Centre to recover any Guildford bombings related material" because of the resumed inquest into the deaths of five people in the IRA attacks.
More than 65 were injured in the explosions and 11 people - the Guildford Four and Maguire Seven - were wrongly-convicted in what became known as one of Britain's biggest miscarriages of justice.
Files taken from Surrey History Centre in Woking that could be relevant to the pub bombings included information sheets on and photographs of wanted people from 1967 to 1974; a major incident handbook from the 1970s; a file dated 1973-75 covering actions in dealing with incendiary devices; and photographs of the interiors and exteriors of the two bombed pubs - the Horse and Groom and Seven Stars.
Other material removed that related to the day-to-day operations of the force over decades included retirement certificates, pocketbooks and photographs of the Operations Rooms.
'Removed by appointment'
The letter from Christopher Stanley at KRW Law to Ian Pollard, senior investigating officer in charge of the Guildford pub bombings, requested confirmation that files were not going to be destroyed and if police intended to destroy material, they refrained.
It also asked on what and whose authority the material was taken from the archive.
The "failure to confirm the retention, independent auditing and storage of the material described in the BBC news report may result in an application to the High Court in Belfast," it said.
Surrey Police said the force stood by a comment issued last week in which it said archivists agreed the files would be removed "by appointment".
A statement said no files had been destroyed and material would be audited against relevant legal guidelines before being returned, where possible, to the history centre.
After the BBC revealed the removal of the files, Surrey Police and Crime Commissioner David Munro said the actions of police were "entirely appropriate", adding: "We have been informed that very little of the material in question relates to the Guildford pub bombings."
The complete list of files taken is not known, but from those listed in the memo, those that could be relevant to the bombings, based on date and subject, include the following:
- Surrey Constabulary Major Incident Handbook c 1970s
- Photograph album of interior and exterior views of the Horse and Groom after the IRA bomb, 5-6 October 1974
- Photograph album of interior and exterior views of the Seven Stars after the IRA bomb, 5-6 October 1974
- Photographs of the aftermath of the Guildford pub bombings by Terry Fincher, copyright Photographers International, 1974
- File of papers relating to the operational activities of Surrey Police including... dealing with bomb threats, 1965-88
- File of papers relating to the operational activities of Surrey Police, including the years 1968-1976 and including reports and investigation of crimes, 1915-88
- Folder of Surrey Constabulary crime information sheets, with photographs and descriptions of people wanted for criminal offences, 1967-74
- Folder of papers relating to actions dealing with hijacked aircraft, incendiary devices and letter bombs, 1973-75
- Ninety pocketbooks of PC, later Det Con, later Det Sgt, later Det Insp, later Det Supt Nicolas James Brent, 1961-1991
- A set of crime scene photographs of the immediate aftermath of the explosions and destruction, 1974
Most were apparently retained under General Data Protection Regulation (GDPR), Management of Police Information (MoPI), Multi-agency public protection arrangements (MAPPA) and Association of Chief Police Officers (ACPO) guidance.
Photographs by Terry Fincher, war photographer and Fleet Street journalist, were open and viewed by the BBC last September.
However, they were held by police as it was "unknown if Terry Fincher served with Surrey Police", the memo said.
Mr Fincher's daughter, Jayne Barlow, who holds his work in a separate archive, said the photographs should not have been in Surrey History Centre and her father would have given the police press office complimentary copies of photographs which was "the usual thing to do during that period".
She said: "Prints were supplied without any angle of being involved in the politics of a story and not for their reproduction. Terry worked as a neutral photojournalist."