A leading law firm gave the warning after insurers won a partial victory in a judgment that found only some sufferers could recover damages for the injuries they sustained at work decades ago.
The three judges were unable to agree on a High Court ruling in November 2008 - hailed as a victory for the victims - that employers' insurers at the time of exposure were liable to pay out on claims for mesothelioma caused by exposure to lethal asbestos in the workplace.
Instead, they found that in some cases the responsibility lay with the employers' insurers at the onset of symptoms, which in some cases is 50 or 60 years later.
Lawyer Helen Ashton from Irwin Mitchell, who represented one of the lead claimants in the case, said that although she was delighted the judgment had found in favour of her client, for many people in a similar position this long-awaited, complex judgment would cause more upset and uncertainty.
She said it is now a matter of pot luck as to which victims will be compensated and it will even leave business and insurance companies unsure of where they stand.
"This may yet impact on the taxpayer," she said, because all mesothelioma victims exposed at work who cannot bring a claim are entitled to a one-off payment from the Government.
Ms Ashton also confirmed that the news received a mixed response from her client Ruth Durham, who had continued the legal battle in memory of her father Leslie Screach, the first person in this litigation to bring a claim.
Mrs Durham said that although her father had died from the fatal lung disease in 2003, after being exposed to the deadly asbestos fibres between 1963 and 1968 while working as a paint sprayer in west London, she had wanted to see justice done for him and other mesothelioma sufferers now and in years to come.
Ms Ashton said: "Without a uniform judgment, it remains unclear which victims are entitled to access the justice they deserve, and it really is pot luck.
"For many, it will mean delays, more legal uncertainty and more confusion, as the very wording of their employers' insurance policies would need to be reviewed to see whether they can make a claim or not.
"And, most tragically, it has added another layer on to what is already a complex claim, meaning that many victims of mesothelioma who have been awaiting the outcome of this appeal decision may not live long enough to know if their families will receive the compensation they need to provide financial security when they are gone."
Mrs Durham said: "Though I am relieved to hear of today's court decision, which will see justice done for my father and some other mesothelioma sufferers, I think it is very sad that there is now a divide, with some victims and their families being compensated, and some not.
"I had hoped to be able to see this through and have a good outcome for all those who, like my dad, suffered so terribly because of someone else's negligence.
"We had been very close, and really were good friends. During the Second World War, Dad learned to use sign language and when I decided to learn, we used to practise together.
"It became our special way of communicating with one another and when he was diagnosed with cancer, he couldn't bring himself to tell me directly and just made the sign for cancer to let me know the terrible news.
"I miss him every day and no sum of money will ever bring him back or make up for what he went through."
Ms Ashton added that the ruling also had important implications for employers and local councils.
She said: "This outcome not only impacts on the people who are dying from this deadly disease, but also raises concerns for some employers still in business, and local councils who may find there is a black hole in their insurance cover."
The original nine-week High Court battle examined a number of cases where the insurers refused to pay out.
They included Charles O'Farrell, a retired member of the Unite union who died in 2003 after being exposed to asbestos while working as a steel erector from 1964 to 1967 for Humphreys & Glasgow, which was insured at the time by Excess Insurance Company.
The employer ceased trading in 1992.
Excess Insurance argued that it was not liable to pay out because, according to the wording of their policy, employees had to "sustain injury" at the time they were working for the employer.
The Court of Appeal decided that Mr O'Farrell did not "sustain injury" until he developed mesothelioma many years later.
Unite joint general secretary Derek Simpson said: "This is the ultimate insult for people suffering, or who have watched a loved one suffer, a painful and degrading death from industrial disease.
"Insurers banking premiums and then escaping paying out compensation by relying on policy small print is obscene.
"Asbestos victims now face more uncertainty, which is the last thing they need. Unite will continue the legal and political fight to achieve justice for our members and all victims of asbestos.
"At a time when the Government is seeking to save money, this decision will prevent the DWP (Department for Work and Pensions) being able to recoup state-funded benefits from insurers, which will inevitably lead to more pressure on public funds."
Head of asbestos policy at Thompsons Solicitors Ian McFall said: "Insurance companies sold policies to cover risk. Now that risk has become reality, they have resorted to picking apart the words in their own policies.
"This decision means some insurers are required to pay while others are not, depending on words such as "injury sustained" or "disease contracted" used in insurance contracts written decades ago.
"Try explaining that logic to people diagnosed with fatal illness caused by the negligence of their employers. This leaves a black hole in the protection that employers' liability insurance was intended to provide."
Mr O'Farrell's daughter Maureen Edwards said: "My dad died a painful death from mesothelioma. Watching him suffer was agonising for all of his family.
"His employer's insurers forced this fight to avoid paying out compensation he had already been awarded. The insurers' attitude is difficult for us to understand.
"My dad would have been disgusted by the lengths the insurers have gone to to get out of paying."
Lord Justice Rix, giving the lead ruling, said six cases had been examined to decide on the issues involving around 6,000 mesothelioma victims and their families, their employers and the insurers.
"This appeal asks the question as to what has to happen in any particular policy year to make the insurer on risk during that year liable to respond and so to indemnify the employer insured.
"Is it the tortious exposure to asbestos which has caused the mesothelioma that must occur in that policy year? Or is it the onset of mesothelioma itself which must occur in that policy year?"
He said the body's defence mechanisms can result in a person exposed to asbestos living for 35 years without passing a stage where a court would say that mesothelioma had begun.
"However, because of the long time-lag between exposure and the onset of the disease, the incidence of mesothelioma is still increasing and is expected to go on increasing for a few years yet, before reaching its peak and then declining."
He added: "Moreover, the health difficulties which working with asbestos has caused and the huge liabilities which asbestos-using industry has over the last half century or so incurred have meant that many firms, even once great companies, are no longer in business, or survive only in a state of insolvency.
"This has meant that there are, unfortunately, mesothelioma claimants and the dependants who are unable to obtain compensation for injury and damage which their employment has brought upon them."
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