A watchdog has accused appliance company Whirlpool of "multiple failings" in dealing with customers caught up in a safety alert concerning tumble dryer fires.
Which? has called on the US company to "clean up its act and treat customers fairly" as the result of an undercover investigation into its handling of the modification of millions of dryers.
Manufacturers Hotpoint, Indesit and Creda are in the process of fixing dryers across the UK after parent company Whirlpool notified customers of a widespread safety defect last October.
Faulty tumble dryers, in which excess fluff can catch the heating element in the machine and cause a fire, have been linked to a number of blazes in British homes.
Which? said it discovered delays, confusion and the withholding of information following undercover calls to Whirlpool, a survey of 800 affected customers and analysis of 40 case studies.
Which? said Whirlpool staff consistently claimed it would take eight to 12 weeks to obtain a customer ID before anything could happen - something the consumer group believed could be achieved at the push of a button - while 32% of those who opted for a repair were told they would have to wait six months or more.
Mystery shoppers posing with a nine-month-old dryer were repeatedly told to take up a claim for a replacement with the retailer, however many of Which's case studies tried this route and were told to go back to Whirlpool.
Which? has published the details of affected models on its website, something Whirlpool had "still not done" in favour of asking consumers to use a model checker on its own website.
A survey by the consumer group found 62% of affected customers were concerned about using their dryer while waiting for a repair, but "numerous" call handlers said there was "nothing to worry about" as long as safety instructions were followed.
Consumers were faced with a decision between lengthy delays for a repair or paying for a replacement at a reduced price.
One in five customers (20%) said they felt they had no choice but to pay for a new machine and 33% said that, given the option, they would rather pay for a replacement than wait so long for a repair.
More than half (54%) of those surveyed felt dissatisfied with the way Whirlpool had handled this situation, increasing to 80% of those who had to wait six months or more for a repair.
Which? is calling on Whirlpool to clearly list all 127 affected model numbers on the front page of its website with details of how customers can get help, speed up the customer ID number process and stop staff directing customers back to retailers.
Which? director of policy and campaigns Alex Neill said: "Whirlpool customers rightly feel dissatisfied with how they've been treated, being faced with delays, confusion and a lack of information.
"Whirlpool must clean up their act and sort this mess out.
"This case, affecting millions, clearly highlights the problems with the current product safety regulations. The Government must act swiftly to simplify the system and close the loopholes that allow companies to leave consumers without the basic information and advice they need."
Whirlpool claimed there were "a number of inaccuracies" within the Which? report, but said: "Any instances which are inconsistent with our high standards will be investigated."
The company added: "Whirlpool's response to the tumble dryer issue is at an unprecedented level, and our staff are working round-the-clock to ensure we're able to resolve the matter as quickly as possible for our customers.
"The safety of our customers is our number one priority. We are committed to doing everything we can to ensure that the modification programme is being carried out in a safe and timely manner and we are continually looking into alternative options which will allow us to progress the programme at a faster pace."
Whirlpool added: "As we have repeatedly explained, we strongly believe that an online checker such as the one we have created offers a much easier solution for consumers than a lengthy list of model numbers. We believe that publishing a list of model numbers risks confusing consumers.
"Our advice to all employees and across all communications is that consumers can continue to use their affected dryer whilst waiting for the modification. However, we require that consumers do not leave their dryers unattended during operation as an extra precaution, i.e. do not leave the house or leave the dryer on whilst asleep.
"Additionally, consumers should check and clean the filter after every cycle and ensure proper dryer venting, as directed in the original operating manual."