A consumer group is calling for the urgent publication of a report into Whirlpool’s fire-risk tumble dryers, amid fresh concerns about the manufacturer’s repair programme and its handling of an issue that may have left up to 500,000 potentially dangerous machines in UK homes.

Which? revealed it had been contacted by more than 30 consumers whose supposedly “fixed” tumble dryers had caught fire, produced smoke or the smell of burning. In some cases this appeared to be as a result of fluff catching on the heating element – the issue the modification was designed to fix, the consumer group said.

Whirlpool insists there have not been any reports of the problem reoccurring with modified machines.

A Whirlpool spokesman said: “We have total confidence in the tumble dryer modification, which was extensively tested before and after being implemented. UK regulatory bodies have repeatedly concluded that the modification is the most effective way of rectifying this issue. We thoroughly investigate all concerns relating to our products as soon as they are reported to us. We can confirm there have been no reported incidents where the modification has proven to be ineffective.”

However, one customer provided Which? with a report from a Whirlpool engineer that stated this as a cause after her modified machine started to produce smoke.

Whirlpool issued a safety warning in 2015 after it found its Hotpoint, Creda and Indesit dryers had a fault which made them a fire risk, and launched a programme of modifying faulty machines. It is still mired in controversy over its decision not to recall items that are at risk of bursting into flames.

The government’s Office for Product Safety and Standards (OPSS) was ordered in May last year to carry out a review focusing on the effectiveness of Whirlpool’s approach and its handling of the modification programme.

Which? said affected customers now needed “urgent clarity” about the safety of the repair programme and is calling for the consumer minister to issue a recall if this cannot be guaranteed.

“The regulator’s investigation cannot continue to drag on when serious questions remain unanswered about Whirlpool’s approach to the tumble dryer scandal,” said Alex Neill, Which? managing director of home products. “It’s very concerning that hundreds of thousands of at-risk machines are still in people’s homes, and that there is still uncertainty over whether the repair programme actually works. The OPSS must urgently release the findings of its investigation. If it finds Whirlpool has failed to put the safety of its customers first, the regulator must take robust enforcement action, including a full recall if necessary.”

Whirlpool said it had been unable to fully investigate the allegations made by Which? “as it has failed to provide essential details to support its claims, despite repeated requests for this information. We cannot therefore offer a considered response to Which?’s claims, and we question the reliability of its research methods”.