Tax chiefs stand accused of breaching the human rights of bereaved spouses and the terminally ill by making them wait more than a year for key evidence in compensation claims.
Lawyers say an average time of 383 days to retrieve historic work records by HM Revenue and Customs is denying claimants the right to pursue firms over work-related conditions.
The widow of an insulation engineer killed by mesothelioma after years working with asbestos attacked the "crazy" backlog and pleaded with the Government to speed up the process.
HMRC blames a lack of machines to access records held only on archaic microfilm and a surge in claims spurred by law firm TV ads for the long waits.
Its boss says officials are "scouring the internet" for spare parts to fix the decrepit readers and have given priority to mesothelioma sufferers, who are promised their details in just ten days.
But law firm Irwin Mitchell says it has dozens of clients with other conditions such as lung cancer, or who have lost spouses to work-related conditions, who are waiting up to 18 months.
It said that in such cases the delays were a breach of the right under Article 6 of the European Convention on Human Rights to have civil claims heard "in a reasonable time".
Some with little time to live risked being denied justice altogether, lawyers argued, accusing officials of failing to act on their calls for action to improve the service.
It has emerged that employment records - required to identify employers or insurers liable to compensation claims - were kept on microfilm right up until 1997 when the system was digitised.
HMRC, though, has only 36 operational microfiche machines for the time-consuming searches and even those break down frequently, sparking hunts for parts or engineers with the skills to fix them.
The number of applications for records has trebled from 40,000 a year to 120,000 over the past five years - each requiring on average 20 items to be located.
HMRC said the jump was "driven by a rise in personal injury claims and heavy marketing from the sector" and had put strain on the hardware and the film itself.
A spokesman said it was "working very closely" with the Ministry of Justice and others on ways both to improve the service and "reduce demand for our records" - with "all options" being considered.
Chief executive Jon Thompson has warned MPs however not to expect any "short-term leap" in improvement.
And Irwin Mitchell questioned its claims to "prioritise all requests relating to mesothelioma cases and serious life-threatening conditions (both for living claimants and the relatives of victims)".
In one regional office alone it is handling four cases involving lung cancer, five with other asbestos-related disease and six of people killed by mesothelioma, all of which were subject to lengthy delays.
That suggested there were at least 50 on its books, a spokesman said.
Roger Maddocks, a partner and expert workplace disease and illness lawyer at the law firm, said his experience was that only living mesothelioma victims were granted the 10-day turnaround.
He said: "It is particularly concerning that the backlog for work history requests is running at 383 days, preventing people determining their rights within a reasonable time.
"We believe that the cause of the delays is the decisions that have been made in regards to the storage of data on an obsolete technology that has led to the creation of a labour intensive process to access this data and the lack of equipment to read microfilms.
"We have yet to receive any indication that HMRC is taking any adequate steps to address these serious issues, which are having a significant impact on those who have developed terrible illnesses as a result of their employment, who are desperate for answers from their former employers about why steps were not taken to protect them, and their colleagues, from harmful substances."
Among those caught up in the delays is Marlene Hutchinson, who has been told it will take 18 months to access the records of her late husband, who died of peritoneal mesothelioma in January 2015.
The 67-year-old, from Middlesbrough, has no doubt the rare cancer discovered in a post- mortem examination was caused by Lawrence's exposure to asbestos during a lifetime working as an insulation engineer.
But she is desperate to see someone held responsible for his death, which came just months after the previously fighting-fit 83-year-old first started being ill.
And she said the failure to quickly produce the records - despite her having supplied HMRC with a detailed history - had left the torment hanging over her.
"I thought I would give them everything I could and then it would get done. That is obviously not good enough," Mrs Hutchinson told the Press Association.
The law firm applied on her behalf in April 2015 but have been told the records will not be supplied until August.
"I just want to make someone responsible. To own up. The more you read into it, the more you see that they knew but they were doing nothing. We didn't know, but certainly companies knew.
"I know all the companies he was working for but it's just the dates which can be a little haywire. I had approximate dates for everything from the 1950s right through to when he stopped work.
"I knew it would be months because government departments are never in a hurry.
"But the other day they said it was going to be nearly 18 months which is crazy, especially when I have given them a starter."
She said: "A favourite word these days is closure and moving on and all that.
"I now know exactly what they are talking about. I just want it sorting because it is hanging over you all the time and you know it is going to come back and upset you.
"Surely they can invest a little bit."