Crime discriminates. The poorest people, in the most deprived areas, are more likely than anyone else to become victims. Yet it is at the other end of the social scale that the latest trend in crime-fighting is emerging.

Eldon Road, Kensington, is one of the smartest residential streets in London. A five-bedroom house would set you back £2.6m. At all hours of day and night, a man strolls with a dog along Eldon Road and adjoining roads. He is a private security guard patrolling public streets, hired by residents who have lost faith in ordinary police.

In the north London stockbroker belt suburb of Hadley Wood, it is a similar story – only here the guard patrols in a car, checking every street at least once an hour, 24 hours a day. The patrols do not come cheap – around £1,000 per household per year. And they are divisive: wherever they are proposed, they cause a rift between residents who are keen and those who do not want to pay. If the patrols go ahead, payment is voluntary – so those who opt out get the safety benefit for free. (In some schemes, those who pay up get plaques on their houses – like the signs in medieval cities which showed which homes had paid fire insurance, and which would be left to burn.)

There has been much hand-wringing over ‘gated developments’, new-built middle-class enclaves in deprived areas where high fences and security guards keep out criminals and law-abiding locals alike. Patrols of the kind seen in Kensington and Hadley Wood are even more striking because they take place on public streets. Yet little attention has been paid to them and no one is really sure how many there are. When I researched the phenomenon for the Evening Standard, security industry sources told me that at least 50 patrols operate in and around London alone, mostly in low-crime areas. The number is growing year by year, driven by fear among the haves that they will be attacked in their homes by violent have-nots.

Should we be worried? Metropolitan police commissioner Sir Ian Blair is. He fears the patrols could fragment society. He points out that private security guards, often armed, already protect wealthy neighbourhoods in South Africa and South America – and says it must not happen here. And Labour should worry because the challenge for the left in Britain is twofold – to keep the welfare state strong, and to ensure that it retains the support of the middle class. The biggest threat is that better-off voters should begin to see public services and benefits as a drain on their wallets to help the poor, rather than as vital provision for themselves and their community. People who opt out of the NHS or state education lose their personal stake in ensuring those services remain strong for others. The same must be true for those who no longer rely on tax-funded policing.

One residents’ leader who organises private security patrols told me the sales pitch he uses: ‘You already pay for private health and send your children to private schools. It’s the same with security – if you want a better service you have to pay for it.’ Of course, the message that you get what you pay for applies equally to the public sector. And the spread of private security suggests that better-off voters would be willing to pay more tax if they were confident of feeling safer in return.

The row over the government’s mental health bill shows up a weakness of the parliamentary committee system. The bill aims to strengthen the care-in-the-community regime to prevent the small number of cases where dangerous patients attack, and sometimes kill, members of the public.

A committee headed by a peer decided that proposals in the bill would infringe patients’ human rights. It had been told as much by dozens of mental health charities, medical bodies and patients’ groups. But the bill is meant to protect the public, and the public is one group that committees are not very good at listening to. With the honourable exception of the Zito Trust, few organisations exist to speak up for families of murder victims at such inquiries.

The job of ministers is to balance the views of special interest groups against the needs of the public. And to tilt the balance towards the public.