Which? has formally requested a judicial review of Peterborough Trading Standards (PTS) over its handling of the Whirlpool faulty dryers safety alert.
PTS has been dealing with the alert, which involves a reported 5.3 million dryers made by Whirlpool brands Hotpoint, Indesit and Creda, as Whirlpool's UK head office is in Peterborough.
Fire chiefs warned in October that owners of faulty Whirlpool dryers must stop using them immediately, after one of the machines was found to be the cause of a huge blaze in an 18-storey tower block in Shepherd's Bush in London.
London Fire Brigade said they believed a faulty Indesit dryer was the cause of the August 19 blaze, following a "painstaking" investigation.
Which? said it was "stepping up its action" with the judicial review request to the High Court following PTS's "failure to review the situation in light of this report".
The watchdog said: "Following earlier attempts to get PTS to do the right thing, we now have no choice but to pursue formal legal action to ensure consumers are protected.
"The judicial review will ask the High Court to assess whether Peterborough Trading Standards' handling of the case since the London Fire Brigade's report has been lawful."
Which? said it believed that PTS had failed consumers by not properly carrying out its role as an enforcer of product safety laws.
It said it expected PTS to conduct a fresh, independent assessment of the risks posed to consumers by the faulty dryers that remain in homes and "not shy away from enforcement action if it is needed".
Various dryers made by Hotpoint, Indesit and Creda between April 2004 and September 2015 are subject to a safety notice about the fire risk, which is caused by excess fluff coming into contact with the heating element.
Which? managing director of home and legal services, Alex Neill, said: "We believe that the way Whirlpool has handled the tumble dryer safety issue is absolutely appalling and to add insult to injury Peterborough Trading Standards has failed to do its duty to protect consumers.
"We have decided to step in and take legal action because we want Peterborough Trading Standards to properly protect Whirlpool customers and carry out its role as an enforcer of product safety laws."
Whirlpool said: "The safety of consumers is our number one priority and we are committed to doing everything we can to ensure that the tumble dryer modification programme is carried out in a safe and timely manner.
"We have acted entirely appropriately at every stage of this programme and refute any suggestion otherwise.
"We urge everyone who owns an Indesit, Hotpoint or Creda dryer manufactured between April 2004 and September 2015 to check if their dryer is affected and then register for a free modification if it is.
"Customers can do this using the model checker on two bespoke websites we have created, https://safety.hotpoint.eu/ and https://safety.indesit.eu/, or our dedicated freephone helpline on 0800 151 0905 for the UK, or 1800 804320 for Ireland."
A Peterborough City Council spokesman said: "The safety of consumers is our paramount concern and has been throughout our involvement in this matter.
"An independent review, which began earlier this month, is currently taking place and we would expect Whirlpool to fully comply with the outcome.
"This review involves independent experts in fire safety, product safety and product risk assessment.
"We will strongly defend our position if Which? is granted a judicial review and bearing in mind the on-going independent review, we consider that this action is premature."