At a time when the number of prisoners has exceeded 80,000 for the first time, it has emerged that the use of the new type of suspended sentence orders (SSOs) is resulting in more people ending up in jail.

The revelation was last night seized upon by Home Office critics who said it highlighted the department's confusion over sentencing policy.

The embarrassing disclosure, made in a prison service briefing document marked 'restricted', comes at a time of increasing pressures on the prison estate. The crisis has become so acute that the government has been forced to examine controversial plans to sell shares in new prisons because the Treasury will not provide additional funding.

The briefing document looks at the use of the new suspended orders since they were introduced in 2005. Their supporters argue that they represent a harsher sentence than a community service order and therefore act as a greater deterrent. The idea is that an implicit threat of a custodial sentence, which will be activated if someone reoffends, deters further crimes.

But the document states: 'The use of SSOs has increased rapidly since introduction in April 2005. Recently around 3,000 per month have been given out by the courts. This is nearly double the number assumed in the latest prison population projections.'

Because the orders are subject to strict conditions, many end up breaching them, with the result that they go to jail for minor offences.

The document states that more than 800 people have been sent to prison for breaching their suspended sentence orders between January and August this year, compared with 132 for the whole of 2005. Three-quarters of the orders have been issued in magistrates' courts, nearly half for summary offences such as common assault or driving while disqualified.

Frances Crook, director of the Howard League for Penal Reform, said ministers should have foreseen the consequences. 'It's a symptom of the way the government is trying to use the criminal justice system to deal with social problems,' Crook said. 'It's like asbos. Instead of being proportionate to an offence, they're trying to sort out the whole life of somebody in the criminal justice system, but you can't do that.'

A Home Office spokeswoman defended the use of the orders: 'This means reoffending is addressed more effectively.'