Norwich & Peterborough Building Society (N&P) has requested more time to deal with complaints from customers caught up in the Lifemark scandal.
In letters sent to 189 customers last week, the company has asked to be given until 15 October to resolve their complaints, according to the Mail on Sunday.
Between 2006 and 2009, N&P sold Lifemark bonds branded as Keydata to more than 3,000 clients who invested about £50m combined.
The cash was invested in insurance-related assets quoted on the Luxembourg stock exchange. The bonds have ceased to pay the promised income.
"We are in discussions with the regulatory community regarding issues which we believe will have a bearing on your complaint," the letter states.
N&P was among the biggest sellers of Lifemark bonds, but the debacle has affected some 20,000 savers.
The FSCS was expected to announce last week whether it would compensate them, but has now pledged to do so before the end of the month.
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