The over 50s fashion chain said that like-for-like sales in the 13 weeks to December 29 dropped 7.8 per cent, while total sales plunged 8.1 per cent.
In store alone, comparable sales tumbled 11.1 per cent.
The lacklustre figures come after a December profit warning sent the Wakefield-headquartered firm’s shares crashing.
Bonmarche said at the time that it could slip to a £4m annual loss amid “unprecedented” tough trading conditions.
Chief executive Helen Connolly said conditions on the high street are worse than those seen during the recession sparked by the financial crisis.
It came after trading during the Black Friday week was “extremely poor”, with ongoing subdued demand despite “extensive” discounting. It also blamed Brexit for adding to the consumer woes.
The chief executive said yesterday: “Clearly, in the short time since our last update, macro market conditions have not changed, but I am pleased that the sale stock is clearing well and that trading is in line with our revised expectations.
“In the short term, we continue to focus on ending the year with a clean stock position and ensuring that our balance sheet remains healthy.”
One bright spot was online, where sales rose 22 per cent in the third quarter, although that was slower growth than in Bonmarche’s first half.
Shares were up nearly seven per cent in morning trade to 39.5p.
The high street chain estimates that with a one per cent fall in like-for-like sales in the fourth quarter, it expects to hit the midpoint of its underlying pretax profit guidance range.
Ms Connolly added: “Looking forward, the board remains confident in Bonmarche’s prospects and strategy and we will continue to drive the implementation of our previously outlined plans, maintaining a particularly strong emphasis on increasing multi-channel sales.”
Analyst Maureen Hinton, group retail research director at GlobalData, said: ‘Either it is just not producing a compelling enough autumn/winter range for its customers, or...the demographic is just not interested in adding yet more higher-priced winter garments to their wardrobe.
“Though clothing retailers across the board have been reporting that November was very poor and there has been extensive discounting, most are still producing positive sales for the quarter, even though mainly driven by online, and few have given a profit warning, which makes Bonmarché one of the worst performers over the period.”