Vital information from the medical records of haemophiliacs infected with contaminated blood has gone missing.
The blood products were used in the 1970s and 1980s
People who contracted hepatitis C and HIV from blood products in the 1970s and 1980s have been campaigning to get their medical notes to assist claims for negligence.
However, the Scottish Haemophilia Groups Forum (SHGF) said the absence of key sections could prevent victims from taking legal action.
The SHGF, which represents 365 haemophiliacs, made the claims as it mounted a "campaign for justice" outside the Scottish Parliament.
They are calling on Health Minister Malcolm Chisholm to set up a public inquiry into the situation.
Hundreds of patients were prescribed a treatment made from the blood of
thousands of American donors to help their blood to clot.
But it was later discovered that some of the blood was infected with hepatitis
C and, in a few cases, HIV.
Philip Dolan, chairman of the SHGF, could not say exactly how many people had discovered that sections of their records were
He said: "Some people decided that they wanted to find out more about what
sort of blood product they had got.
The big thing about this is that if you're going to seek to take litigation,
then you need to know what batch number you had
"When they contacted the hospitals, some were told it would take a very long
time, others eventually got their records but parts were missing, particularly
between 1980 and 1985.
"That was the time when US blood products came into this country."
Mr Dolan added that gaps in the records could prevent patients taking legal
action over the mix-up.
"The big thing about this is that if you're going to seek to take litigation,
then you need to know what batch number you had," he said.
He refused to say whether he thought there had been a cover-up but said: "You
can get a bit cynical about your records disappearing.
"If you (a hospital) make a mistake once or twice, fine, but if it gets done
three times, you start to think again."
The Scottish Executive refused to comment on the allegations, saying it was a matter for individual NHS trusts.
However, Mr Chisholm promised to investigate the claims of missing records.
A senior detective from Strathclyde Police is also currently investigating claims of negligence.
Last month Mr Chisholm promised compensation of up to £45,000 for people who contracted hepatitis C from contaminated blood given to them on the NHS.
We have undergone a number of inquiries... and they have found that we were not in error
Blood Transfusion Service
But the minister has said that no one will get any cash until the executive has resolved an ongoing argument with Westminster over the ex-gratia payments.
He said on Thursday that those discussions were moving forward.
Demonstrators also called on the minister to extend the compensation scheme to families of dead hepatitis C patients.
Ian Franklin, the medical director of the Scottish National Blood Transfusion Service, said the NHS was not at fault for the infections.
"We have undergone a number of inquiries to discover whether we were culpable and they
have found that we were not in error," he said.