Illegal skin-whitening creams are being sold by high street cosmetics shops despite a number of prosecutions, a BBC undercover investigation has revealed.
Shaba Hair and Cosmetics stores have been fined for dealing in creams containing hydroquinone but researchers found outlets continuing to sell them.
Products containing hydroquinone can damage the liver and nervous system.
Trading Standards officials said there was "no excuse" for selling the creams. Shaba declined to comment.
Skin-lightening products containing hydroquinone are widely used throughout India and sub-Saharan Africa - although some countries have outlawed the ingredient.
Shaba director Banaras Hussain has been prosecuted for selling the banned creams at his shops on three previous occasions - in Enfield, Dalston and Peckham.
Made in the Congo
He was fined £11,792 over the Peckham sales alone, and is due in court on 1 April for sentencing after pleading guilty to 33 offences related to the Dalston shop.
But after a tip-off, the BBC found Shaba outlets continuing to deal in banned skin lightening creams under the auspices of Mr Hussain.
At Shaba Hair and Cosmetics (Peckham) an undercover researcher was sold a jar of 'Caro Light' cream priced at £9.99 that listed hydroquinone as an ingredient.
Manufactured in the Democratic Republic of Congo, when tested it was found to contain 4.6% hydroquinone - more than twice as powerful as the strongest medicine containing hydroquinone licensed for prescription for medical purposes by a UK doctor.
The cream was sold in a black bag from under the counter. When the researcher asked for a receipt, an assistant asked Mr Hussain in Urdu: "Brother, I have given her the goods and now she wants a receipt. Should I give it to her or not?"
In response, Mr Hussain tore off the name and address of the shop before handing the receipt over.
At Shaba Cosmetics Ltd in Dalston, a member of staff informed the BBC that three products displayed on the shelves contained hydroquinone - despite it not even being listed as an ingredient.
The worker admitted the sale of the product was not allowed. Two of the creams were subsequently found to contain the chemical.
When confronted with the evidence, Mr Hussain made no comment.
'I kept on using it'
Sarah Oladokun, a 19-year-old beauty blogger from Peckham, used skin-lightening creams when she was younger. She said: "My skin became patchy, very uneven, which then caused problems for me because I didn't know how to balance it out.
"So instead of me stopping I would continue to put more on the darker areas.
"It became very sensitive as well."
Dr Anjali Mahto, a consultant dermatologist at the British Skin Foundation, warned: "It's really worrying actually. You're liberally applying these treatments, and you don't know how much of these chemicals are contained within them.
"It's incredibly dangerous in terms of long-term effects."
Paul Gander, team leader of Southwark Trading Standards, said he would expect to seize about 1,000 products on a typical period of enforcement action.
"In Southwark we've done test purchasing and in about 50% of the shops they appear willing to sell it if pushed," he said.
"In certain areas the problem seems to be quite severe."
He added: "There is no excuse for selling this product."