Food watchdogs have issued an alert after finding that a chemical marketed online as a health supplement was similar to industrial-strength bleach.
'Miracle Mineral Supplement' is 28% sodium chlorite - which becomes bleach when mixed with citric acid.
Even taken as instructed, experts say it can cause severe vomiting and diarrhoea - and mixing it wrongly could lead to respiratory failure.
The Food Standards Agency is seeking to track down any UK-based sellers.
The supplement, which claims to have beneficial effects against a wide range of illnesses, ranging from HIV and hepatitis to H1N1 flu, has already been the subject of warnings from the Food and Drug Agency (FDA) in the US.
Now UK consumers are being urged to dispose of the supplement as soon as possible, and help the Food Standards Agency and local authorities find suppliers in this country.
It is still apparently on sale here through a number of sites, one offering a 100ml bottle for £33.
A spokesman for the Food Standards Agency said: "People should not take Miracle Mineral Supplement or Miracle Mineral Solution.
"This product is equivalent to industrial-strength bleach.
"The agency is working with local authorities across the UK to stop this product being sold. If anyone finds this product on sale please get in touch with your local authority trading standards department as soon as possible."
In the US, the Food and Drug Administration (FDA) has reported cases of severe nausea and vomiting among people taking the supplement, even though they had mixed it according to the instructions provided.
When sodium chlorite is mixed with acid, it becomes chlorine dioxide, the active ingredient in bleach.
The chemical is far more potent than household bleach, and if users failed to follow dilution instructions properly it could mean an even more potent concentration ends up in the body, said experts.
This could cause damage to the gut and red blood cells, potentially leading to respiratory failure.
Because sodium chlorite is not licensed as a food supplement in the UK, local authorities have the power to take legal action against any company supplying it from an address in their area.
The BBC approached one UK-based company selling the supplement via the internet, but no response has been forthcoming.