Newham council's bid to ship hundreds of housing benefit recipients out of London was met with a wave of shock and "moral outrage" last month. Claim and counter-claim followed as Conservative ministers clashed with their Labour counterparts. Both parties agreed on one thing: families are harmed when ripped up from their roots, divorced from support networks and their children moved away from their schools.

Ministers reacted quickly with a pledge to ban such a harmful idea by introducing new rules. Such a safeguard is welcome, especially if extended to families subject to child protection measures, as recommend in my investigation for the housing network into the link between multiple moves and child deaths.

There is, however, emerging evidence of another potentially harmful effect of the welfare reforms for which no extra safeguards have yet been pledged. This new worry was explained by a senior council officer and stems not from some theoretical plan or policy but from issues raised in a recent real life case.

John is a 30-year old homeless man with a history of violent behaviour including a string of convictions for actual and grievous bodily harm. The advice agency helping John knew that he qualified for housing benefit but not social housing.

A change in the so-called shared accommodation rate housing benefit (SAR) rules had effectively closed off the most obvious option for someone with John's history: a self-contained privately rented flat paid for by housing benefit. The rule change, which came into effect in January, raised the age at which welfare will cover the cost of such accommodation from 25 to 35.

This left his advisors with one practical but worrying problem: to help John to rent a room in a shared home with housemates who are oblivious to his past and the risk he poses ? or to leave him on the streets. "The support worker who asked me for advice was in a dilemma," the council officer told me about John's case. "[John's] only option was the private sector but he was dangerous. The only other option was to leave him to sleep rough".

The government does have a safety net in place to protect the public from potentially dangerous ex-offenders and has done for some time. Those who pose a "serious harm" to the public ? about 3,000 cases ? are automatically exempt from the SAR restriction. But such a safeguard would not catch cases like John's. It only applies to category two and three offenders under the Multi-Agency Public Protection Arrangements (MAPPA) in England and Wales.

This leaves about 45,000 ex-offenders who are not exempt, even though some are considered dangerous. Raising the SAR bar from 25 to 35 has also caught a much larger, potentially dangerous demographic, according to the council officer I spoke to.

"We have had this same problem with under 25s," he said. "But a lot of our clients with a history of homelessness and violence are over 25 and have a history of being unable to live in shared accommodation." A Department for Work and Pensions (DWP) circular confirms that most people subject to MAPPA are over 25.

The DWP does have another safety device which it claims should catch potentially dangerous housemates such as John. Those not covered by the serious harm exemption can apply for discretionary housing payments (DHP) when appropriate.

But evidence suggests that the DHP may not be up to the job. Payments are awarded on a short-term basis and can be withdrawn after a few months. Landlords are therefore understandably reluctant to take on DHP-dependent claimants and housing advisers consider it bad practice to suggest accommodation for which rent payments cannot be guaranteed long term.

The potential implications of John's case are nothing short of alarming. Sharing a flat or house with a stranger is an increasingly common affair; it is many medium-income earners only option in towns and cities were rents are spiralling upwards. The least we might expect from ministers seeking to slash welfare bills is for them to fulfil that most basic role of the state: protecting their citizens from harm.

The government reacted quickly to the Newham debacle with a pledge to protect families threatened with the harm of being forced to move. They should act with similar speed to protect house and flat sharers. It is already aware of the risk that ex-offenders can pose to house sharers. John's case indicates those risks have now become real. The worries raised by John's case might be anecdotal at this stage, but they should not be ignored.

? Some names and identifying details have been changed

Keith Cooper is a journalist and researcher, currently studying for a PhD in public policy and philosophy. He is the former deputy editor of Inside Housing magazine

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