Linda Walker, 48, head of food technology at New Park special school in Salford, fired the gas-powered pistol up to six times at the teenagers, after they emptied a washing-up liquid bottle full of water over her son’s car. She claimed that she had been driven to take action after the teenagers had repeatedly insulted her family and vandalised her garden.

She told police that she had received a series of nuisance telephone calls, in which her 17-year-old son Craig had been called a “poof”. She also said that the youths had broken the wing-mirror of the car belonging to her other son, James, also 17, and that they had broken into her garden shed repeatedly.

Ms Walker was sentenced this week to six months for the firearm offence, and one month for affray. The two sentences will be served concurrently.

The verdict has met with outrage. The Daily Express ran the story under the headline: “How can this be justice?” And, in an editorial this week, The Sun said: “Why the hell has she been sent to prison for six months?...

Vandals and yobbos go free. A decent woman does not.”

Norman Brennan, head of the Victims of Crime Trust, who is a police constable, said: “What forced a woman of Ms Walker’s background and calibre to take the action she did? Is it because she’s a violent criminal? No.

It’s because she feels let down by the criminal justice system.”

Farrhat Arshad, Ms Walker’s barrister, said: “She had been pushed to the edge. But she now realises that it wasn’t the best way to deal with the situation.”

Ms Walker has told Ms Arshad that she hopes to continue teaching. She was suspended from her post prior to the police investigation. Staff at New Park were not available for comment. But there will now be an internal disciplinary investigation.