Last month, the government voted in favour of the “full disclosure” of all documents held on the tragedy in Hillsborough. Those documents are now being examined by the Hillsborough Independent Panel (HID).

The families of those who died at Sheffield Wednesday’s football stadium in 1989 – 96 Liverpool fans were crushed to death in the stands as they watched an FA Cup semi-final between Liverpool and Nottingham Forest – have long campaigned for access to more detailed reports on the incident.

There have been accusations of an “establishment cover-up” by the Conservative government at the time, with many families still in the dark about exactly how and why their loved ones died.

The new revelations were considered so important by the HID that it took the decision to inform the affected relatives now rather than wait until its full report is published next year.

Sheila Coleman, of the Hillsborough Justice Campaign, said: “This proves things are being kept from the families and have been for 22 years.”

Taking tissue without notifying relatives was legal at the time of the tragedy, but went on to be banned by the Human Tissue Act 2004.

It is reported that the tissue was taken to help establish cause of death of the supporters who did not display obvious signs of being crushed.

Professor Bharat Jasani, head of pathology at Cardiff University, explained to The Mirror newspaper that tissue samples are usually no more than one centimetre squared, adding: “A pathologist may feel the need to examine further the cause of death when a visual examination is not enough.

“A sample would allow a thorough investigation under the microscope.”

In a statement HIP chairman the Bishop of Liverpool, the Right Rev James Jones, said the panel would ensure the tissue is dealt with “respectfully”.

He added: “I am sorry this additional distress has been caused to some of the Hillsborough families who have suffered greatly already.

“The panel believes that it is right that affected families should have the chance to find out about this now.”

The families of the victims have argued that the disclosure is significant as it reveals a culture of cover-up around the disaster, and that the bereaved have not been treated appropriately.