East London shopkeepers are being urged to stop selling products which contain corrosive substances to young people following several violent attacks.
The voluntary scheme set up by Hackney Council would see traders refuse to sell acid or ammonia if they believe it may be used to cause harm.
Mayor of Hackney Philip Glanville said the scheme was started to "keep these dangerous substances off the street".
There is currently no age restriction on buying such items in the UK.
Products which contain acid or ammonia such as drain cleaner have been used in a number of recent attacks in the capital.
Four shops signed up to the scheme when it was started last year, but Mr Glanville said Hackney Council planned to expand it across the borough.
Anybody who signs up is given training by council officers and provided with a sign saying they will not sell corrosive products to people aged under 21.
Earlier this year it was revealed there has been a sharp rise in the number of attacks involving corrosive fluids in London.
Last year it was used in 454 crimes compared to 261 in 2015, figures from the Met Police show.