On Thursday evening, London was hit by five separate acid attacks. Two teenagers, ages 15 and 16, have been arrested.

London is a big city, so when a crime that doesn't kill anyone makes news, it's a big deal. But this isn't an isolated incident. Consider the BBC graph below.

That up-curve tells a tale. Acid attacks are becoming a serious problem on London streets.

So what's behind it? I think three things.

First, acid can be carried without a legal warrant. Londoners are able to go into a store and then legally walk around with the corrosive substance they have just bought.

That's not the case with knives or other possible weapons such as baseball bats (you need to be playing baseball). But while it would be impossible to ban the sale of acids (they are used in cleaning goods), English law could be changed to make it an offense to carry a corrosive substance without justification. Some suspects would inevitably get around this law, but it would give the police greater powers to address threats on the street.

Another problem?

At present, the criminal offense that acid attacks should fall under — "assault occasioning grevious bodily harm (GBH)" — is often charged at the lower offense level of "assault occasioning actual bodily harm (ABH)." The U.K. prosecution service defines GBH offenses as those causing "really serious injury," and ABH offenses as those causing "serious injury."

The problem here is that the U.K. has too few prosecutors, and GBH prosecutions are longer and more expensive. As such, the British government needs to change the law so that acid assaults are mandatorily classified at GBH level. Minimum sentences and hiring more prosecutors would also help.

Third, acid has attained social power among gangs and other criminals. The use of mopeds to steal other mopeds, as was the case in these latest attacks, is also a contributing factor here. Mopeds are popular with criminals in enabling efficient travel through London's roads and back alleys. They are also very useful for escaping the car units of London's Metropolitan Police Service.

A fourth challenge is that the police are under pressure to avoid chasing mopeds. This is due to an incident in which a teenage criminal, Henry Hicks, crashed and was killed while being pursued.

I say too bad. The British government should grant authority to police officers to aggressively chase suspects. If they want to use mopeds to commit crime, let them risk the whirlwind.

Ultimately, however, until the U.K. takes action, the curve is only heading one way: up.