Pre-election promises aren’t worth the ballot paper they are written on, so don’t take too seriously the sinister spectacle of Labour and the Tories espousing the same populist cause.

The populist knee-jerk of the moment is the old chestnut of how far a householder can legally go to protect his property and the people living there. We had all this 10 years ago with Tony Martin, the Norfolk farmer who shot and killed a teenage burglar. Thieves had repeatedly targeted Martin’s isolated farm and, although he had been banned from holding a firearm permit, he had acquired a shotgun. One night he heard intruders and, as they ran off, he shot the teenager in the back. He was jailed for life, but released after just five years.

Politicians, policemen and readers of the Daily Mail were outraged that Martin was imprisoned simply for protecting his property. They conceded that the sentence for burglary wasn’t actually death, not yet anyway, but the kid had had it coming and good riddance. The law takes a different view. A householder is allowed to use ‘reasonable’ force in self-defence, it maintains. Shooting someone in the back as they run away, however, does not qualify as self-defence – or even as the ‘reasonable’ use of force.

Martin spent the next few years behind bars, a lesson for everyone with a hankering to become a vigilante.

We are now having the same debate following the imprisonment of the brothers Munir and Tokeer Hussain. A burglar, abetted by accomplices, had tied up Munir and his family and threatened them with knives. The brothers had somehow got free and chased the burglars out of the house and down the road. They had caught one and beaten him senseless with a cricket bat, leaving him brain-damaged. This was not a ‘reasonable’ use of force, the court held. One brother was given 30 months in prison, the other 39 months – light sentences for the serious offence of causing grievous bodily harm.

Innocent men are in prison, some pundits thundered when the sentences were announced. The brothers’ actions arose from the natural and manly impulse to protect loved ones from lowlife scum. They were right to take the law into their own hands.

Labour and the Conservatives, sensing a vote catcher, have both now said they will review the law in such cases if they win the next election. Home secretary Alan Johnson, speaking on the BBC on Sunday, said he was ‘uncomfortable’ with the sentences. His Tory shadow, Chris Grayling, has said much the same.

Despite these pre-election promises, there are unlikely to be significant changes to the law. The two brothers, of course, had every right to be furious that Munir’s wife and children had been threatened by intruders into his home, but a mark of our civilisation is that the business of punishment is left to the due processes of law. The police will investigate, charges will be brought, a judge will direct and a jury will deliberate.

Crazed good guys don’t go around taking out the bad guys. That’s the stuff of Hollywood – or anarchy.