The Co-operative Group will come under further pressure this week as retail market share figures tomorrow show it has lost further ground to rivals in recent months, a report has suggested, after four months of falling sales.

The Kantar WorldPanel report is expected to show the Co-operative's food retail market share down to around 6.2%, from 6.6% a year ago.

Meanwhile, the group remains under scrutiny over its treatment of small investors in its permanent interest-bearing shares, who have been told their interest payments are suspended and they face losses of up to 40%.

Another report yesterday revealed one pensioner was told by a bank manager on May 13, three days after the downgrade of the group's debt to "junk" status, there was "no need to be concerned".

A month later the bank announced one-third of its £1.5bn refinancing was to come from bondholders including the small investors.

The Co-op said bondholders had been referred to a helpline and to the need for financial advice.