The Co-operative Bank reassured pensioners that their investments were safe a month before announcing plans to slash their savings as part of a last-ditch bail-out.
In emails seen by The Sunday Telegraph, a manager at the Co-op Bank told a worried pensioner that "there is no need to be concerned" about a £50,000 investment.
The email was sent on May 13, just three days after the ratings agency Moody's downgraded the bank to "junk" .
The following month, the Co-op suspended interest payments to pensioners and told savers they faced losses of at least 40% on their investments. The bank also said it had a £1.5bn capital shortfall.
The pensioner wrote: "I am a member of the Co-operative Group and my wife and I ... are extremely fearful that we are about to lose all of this very important retirement savings nest-egg, the income from which we rely upon. We are very, very worried."
The manager replied: "There is no need for you to be concerned. We do acknowledge the need to strengthen our capital position ... and we have a clear plan to drive this forward. I hope this provides some reassurance."
At that point, the bank was in discussions with the regulator about the size of its capital shortfall. A month later it revealed it needed £1.5bn, £500m of which was to come from enforcing losses on bondholders.
Including large investors, the bondholders have £1.3bn of debt, £65m of which is with 15,000 pensioners and small savers.
Last Friday, the Co-op offered bondholders an olive branch by promising to roll up interest and pay it out if the rescue plan is successful.
Co-op sources claimed that, if bondholders refused to accept the terms, the bank would be put into "resolution" - potentially wiping them out.
Details of the deal will be published in October.
Vince Cable, the Business Secretary, told The Sunday Telegraph that MPs should investigate the crisis. "I am sure the Treasury Select Committee will be wanting to have a careful trawl through what has gone on," he said.
The Co-op's £1.5bn capital hole virtually wiped out its entire £1.7bn equity base, leaving it almost insolvent.
Many of the pensioners affected rely on the interest the bonds pay, which ranges from 5.55% to 13%.
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