IT took Lawrence Storer about three minutes to jump into his car and take off after the man who had just robbed him at gunpoint in the Thai restaurant he owns in Tampa, Florida.

Storer, 36, spotted his assailant, Shantavious Wilson, a few streets away. He drove down a one-way street the wrong way and swerved his car into Wilson, knocking him down and killing him.

Storer’s acquittal on manslaughter charges this month has added a new twist to a spreading American debate about the use of force in so-called self-defence.

What are known as the “stand your ground laws” allow Americans to use deadly force against anybody threatening them. But critics call them “shoot first” laws that encourage vigilante justice and lead to tragic errors.

They have also become known as the “shoot the Avon Lady” laws, for fear that door-to-door saleswomen could be mistaken for trespassers.

When a Florida jury set Storer free despite undisputed evidence that he deliberately rammed Wilson with his heavy 4x4, there were cheers at his restaurant and passing motorists honked their horns in approval. Yet the jury’s finding that Wilson’s death was an “excusable homicide” has further blurred the legal lines between crime and punishment in America.

Last October Florida became the first state to adopt a “stand your ground” law giving people the right to shoot intruders who enter their homes, cars or businesses. The law abolished a requirement that anyone in a public place was obliged to try to run away if menaced, rather than resort to deadly force to protect themselves.

Since then 14 states have followed Florida’s example, provoking angry exchanges as critics complain that gun owners have been given a “licence to kill”.

Despite warnings that the new laws would encourage mayhem — with suburban neighbours gunning each other down every time they saw a shadow — there have so far only been 14 cases in Florida where the laws have been invoked. Yet the evidence from those cases has fuelled opposing arguments about the opportunities the laws provide for “getting away with murder”.

When Oklahoma passed its new laws in May, Kevin Calvey, a state legislator, declared they were “going to give the crooks second thoughts about carjackings and things like that . . . they’re going to get a faceful of lead”. But officials in New Hampshire rejected the new laws as dangerous and likely to encourage violence.

“These are not just self- defence bills,” said Jim Brady, the former White House press secretary wounded in the assassination attempt on President Ronald Reagan in 1981. “They go far beyond just protecting one’s home.”

Critics point to the case last month of Jacqueline Galas, a 23-year-old prostitute, who killed a 72-year-old client with his own gun after she claimed he had threatened her.

Police established that the client, Frank Labiento, had written a suicide note and may have been planning to shoot Galas first. When Labiento answered the telephone in his kitchen, Galas grabbed the gun and shot him.

In an arrest report, a local detective wrote that Galas “made no attempt to flee, nor warn the victim that she was going to shoot him”. She did not call for medical help even though Labiento took some time to die. Yet prosecutors last month decided to drop murder charges.

Supporters of the new laws point to the case of Antoine Jones, a 25-year-old Florida ex-convict who on his release went to live with his mother, her boyfriend and their three teenage daughters. After a row, Jones picked up a knife and tried to break into a bedroom where the boyfriend, Sylvester Andrews, 39, and the girls had sought refuge.

A police report said Andrews opened fire when Jones kicked down the door, killing him instantly, but Andrews was not arrested after claiming to have acted in self-defence.

“It’s the criminal element that preys upon the lawful element,” said state senator Alan Cropsey, who sponsored a self-defence bill in Michigan. “Why should you have to retreat from a criminal?” Several of the recent cases have not been so clear-cut. In Clearwater, Florida, Jason Rosenbloom was shot by his neighbour, Kenneth Allen, after a dispute over dustbins. Allen claimed he felt threatened after Rosenbloom tried to enter his house. Allen has not been arrested after claiming self-defence.

The Storer case hinged on whether his chase of Wilson could be said under Florida law to have occurred “in the heat of passion, upon any sudden or sufficient provocation”. The six-member jury cleared him.

“Storer got a judge and a jury,” said Wilson’s father, Augustus. “My son didn’t get any of that.”

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