Millions of owners of potentially lethal tumble dryers have been warned not to use them until the machines have been repaired.
Tumble dryers sold under the Hotpoint, Creda and Indesit brands have been behind a series of fires.
Whirlpool, which owns the brands, had said they were all right to use, providing someone was in attendance.
But Trading Standards ordered new guidance, namely that they should not be used until they are repaired.
A statement on the Whirlpool safety website says: "If your tumble dryer is affected by this issue, then you should unplug it and do not use it until the modification has taken place."
At the same time the consumer group Which? has called for a full recall of all the machines involved.
Some owners have been waiting up to a year for a free repair programme to be carried out.
Fires have been caused by excess fluff, which can come into contact with the heating element and so catch light.
One machine awaiting repair caught fire in London last August, causing a blaze in a tower block that took 120 firefighters to bring it under control.
The dryers subject to the repair programme were manufactured between April 2004 and September 2015 under the Hotpoint, Indesit, Creda, Swan and Proline brands.
Whirlpool freephone helplines: 0800 151 0905 for the UK, or 1800 804320 for the Irish Republic
Whirlpool has written to 3.8 million owners of the affected dryers, but as many as 2.4 million have not responded. The company has written to them again, offering to repair their machines.
A further 100,000 customers have registered, but not yet organised a repair.
"Since the launch of this campaign, safety has been our number one priority," Whirlpool said.
"We have consistently responded to the advice of Trading Standards and continue to do so. Trading Standards have now notified us that updated usage advice should be communicated to consumers and we are implementing this."
Which? called for a full recall programme of the faulty machines.
The consumer group has already launched a legal bid to force Trading Standards to take stronger action over the tumble dryers.
"Fundamentally, we now believe a full recall is necessary, and the Government must urgently address the issues with the product safety system as it shouldn't require the threat of judicial review to ensure that consumers are protected from dangerous products," said Alex Neill, managing director of home and legal services at Which?
"Despite updating the safety notice on its websites, Whirlpool still needs to do a lot more. Our advice is to go straight to Whirlpool to demand your machine is fixed, but also try speaking to the retailer you bought it from."
The Trading Standards office in question - in Peterborough - has said that the threat of legal action was premature.
The London Fire Brigade, which tackled the blaze in Shepherd's Bush last August, said it agreed that owners should not use the dryers until they were repaired.
It said it had already asked Whirlpool to give out that advice.
The Brigade's assistant commissioner for fire safety, Dan Daly, said: "This change of advice could save lives and we are extremely relieved that, after six months of campaigning by the Brigade, Whirlpool has finally brought its advice in line with our own.
"We attend nearly one fire a day involving white goods, and strongly believe that if your appliance is subject to a safety or recall notice, or you think there is something wrong with it, you should unplug it immediately and contact the manufacturer or a qualified repair technician."
Jill Paterson, a partner at Leigh Day, the law firm acting for some of those affected by the Shepherd's Bush fire, said the advice from Whirlpool was long overdue.
"There should have been more urgent action taken to protect consumers - it should not have taken enforcement action by Trading Standards for this to happen," she said.