The Co-operative Group has fallen into the red for the first time since 2013 after writing off the value of its stake in the troubled Co-operative Bank.

The mutual revealed pre-tax losses of £132 million for 2016 as it took a £185 million hit after slashing the value of its 20% holding in the Co-operative Bank to zero.

The Co-operative Bank has been put up for sale amid concerns over its balance sheet strength as it continues to suffer following its 2013 rescue after the discovery of a £1.5 billion black hole in its finances, which left it majority controlled by US hedge funds.

The group posted profits of £23 million in 2015.

It said the move to write off its stake in the Co-op Bank was a "prudent valuation" amid "volatility" caused by the ongoing sale process.

The group gave a cautious outlook for the year ahead, warning: "All of our markets remain fiercely competitive and we face a challenging consumer and economic backdrop."