The Court of Appeal has upheld an insurance claim by Standard Life over the £100 million of compensation it paid out to investors nearly three years ago.
Standard's 11 professional indemnity insurers had taken their case to appeal after losing in the Commercial Court in London last February.
They now have 28 days to seek leave to appeal to the Supreme Court.
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The legal wrangle follows Standard's £102m payout to compensate 97,000 customers who overnight in January 2009 lost 5% of their savings in what the Edinburgh insurer had marketed as a "cash fund".
Standard was later fined £2.45m by the Financial Services Authority for "serious systems and controls failings" that allowed misleading marketing material for the Pension Sterling fund.
The fund, which attracted more than £2 billion by early 2009, was 13% invested in sub-prime mortgages, which had been hit by the Lehman Brothers crash.
It had been marketed as a low-risk, cash-based investment, and the subsequent losses led to hundreds of complaints from investors and a reputational crisis.
Standard earned plaudits by moving swiftly to repair the damage, topping up the fund to restore customers' savings to their previous level. The insurer said at the time that its move "reflected the importance we attach to the long-term relationships we have with our customers".
The fund was renamed, then in 2011 surviving investors were offered a transfer to a Deutsche Bank fund as Standard exited the money market sector.
Standard's insurers, a consortium of 11 European specialists in professional indemnity, declined Standard's claim for the £102m pay-out.
When Standard took the insurers to court in October 2011, it emerged in evidence that former chief executive Sir Sandy Crombie had conceded that the fund's marketing literature had been "hopelessly inadequate".
The insurers argued they were not liable because the payment was not directly related to any liabilities and was not incurred necessarily. They also said it should not be covered if Standard's motivation was partly "to protect the brand or reputation of the company".
Standard's lawyers argued that by voluntarily making the payment it had averted potentially larger losses, and that its indemnity policy covered "taking action to avoid a third party claim or to reduce a third party claim".
Mr Justice Eder, upholding Standard's claim in February, said what mattered was the intended effect of the payment, not the company's motive for making it or to whom it was directed.
Standard says if leave to appeal to the Supreme Court is granted, it is unlikely that an appeal would be heard before autumn 2013.
Shares in the Edinburgh-based firm ended the day up 1.3p, or 0.39%, at 334.9p.