Amsterdam city council is stepping up its efforts to warn tourists about the danger of buying drugs from street dealers following the death of three British tourists last month.

The tourists died after taking what they thought was cocaine but was actually a lethal form of white heroin. At least 14 others have been hospitalised after taking the drug.

The city’s mayor, Eberhard van der Laan, said on Thursday that test kits to check that cocaine is not heroin will be available in at least 30 of the city’s ‘smart shops’ – shops which sell legal highs and smoking equipment.

In addition, special teams will be on the streets selling the test, which cost €2 each. The options for testing drugs are being publicised on matrix boards, leaflets and via social media.

If anyone is found with heroin, they will be urged to contact the city’s health board.

A team of 20 detectives is investigating the case but a television appeal on Tuesday resulted in few useful leads. Van der Laan said every year some 1,000 street dealers are picked up in the city selling fake drugs.