The GMB union has said all 400 Wilko stores will close in early October.
It means there is now the possibility of redundancies for all 12,500 staff at the high-street chain.
The GMB union, which represents more than 3,000 Wilko staff, revealed the damaging update following a meeting with the retailer’s administrators on Monday morning.
Wilko is expected to close another 124 stores next week (Jonathan Brady/PA)
Wilko warehouses in Worksop and Newport are now due to close on Friday September 15, the union said on Monday.
It said 124 more stores are set to close next week, with them set to close between September 19 and September 21.
The retailer had already confirmed that 52 stores would be closing this week, leading to the loss of 1,016 jobs and hundreds more across the business.
It comes after a last-ditch effort by HMV’s boss to strike a rescue deal for the retailer failed.
The high street chain was in discussions with administrators Doug Putman, who bought the entertainment chain, over a deal to buy around 200 Wilko stores in 2019.
GMB said the failure to secure a deal means the remaining offers on the table only involve the possibility of purchasing a number of Wilko store assets, and are not expected to include workers.
PwC, which is overseeing administration, has already agreed a deal worth around £13m to sell 51 Wilko stores to rival B&M.
According to Sky News, fellow discount retailer Poundland is still in talks with PwC in an attempt to buy around 100 shops.
Other high street chains including The Range and Home Bargains have also reportedly indicated their interest in purchasing the Wilko brand or stores.
GMB national officer, Nadine Houghton, said: “This is not an unprovoked tragedy. Wilko should have thrived in a low-cost retail sector that is otherwise strong, but business owners let it collapse.
“Money was taken out of the business for dividends, warnings about what needed to be done to save the business were ignored and advice about what to do to take the business forward was not listened to.
“No worker caused the downfall of Wilco. But they will have to suffer – because the owners will escape unscathed.
“GMB will not stop campaigning to hold the bosses of this debacle accountable.”
Wilko entered administration early last month after coming under pressure from weak consumer spending and debts to suppliers.
Labour’s shadow business secretary Jonathan Reynolds said: “This is heartbreaking news for workers and their families who are hoping for a deal that will protect their jobs.
“Sadly, closed shops have become the norm under the Conservatives, undermining the foundations of our economy and causing local high streets to pay the price.”