The Big Question: Why are our prisons so overcrowded, and how can we tackle the crisis?

Why are we asking this question now?

Jails in England and Wales could be full within a fortnight. The increase in numbers of offenders being locked up appears relentless, with the prison population reaching a record high of 80,846 this week. That includes about 400 who are housed at great expense in police cells and a further handful held in court cells.

There are only some 250 empty beds anywhere in the country in already overcrowded prisons - and those spaces are often hundreds of miles from where they are needed.

The National Offender Management Service is racing to build extra spaces in prisons, with more than 82,500 expected to be open by the end of 2007, but they are being filled almost as quickly as they become available.

There is a palpable sense of crisis at the new Ministry of Justice, which assumed responsibility for prisons last month, with ministers agonising over emergency measures as they work on the assumption that jails could be full by mid-June. One Ministry source said: "You can't exaggerate how serious the situation is - without something radical happening we will be in deep trouble any day."

What could happen next?

Phil Wheatley, the director general of the Prison Service, could be forced to inform Lord Falconer of Thoroton, the Secretary of State for Justice, that his jails are full. Any new offenders would have to be crammed into police and court cells. But that raises further questions. Where would police hold newly arrested people? And how could the courts hold those awaiting trial if its cells are full of newly sentenced criminals? Harry Fletcher, assistant general secretary of Napo, the probation officers' union, said: "If that happens, there is a very real risk the courts won't be able to function."

What options are open to ministers?

They are pressing ahead with a building programme which will create an extra 8,000 spaces by 2012. In the shorter term, they are casting around for temporary accommodation and have even considered leasing prison ships. But these appear to be "sticking-plaster" solutions designed to buy time, and there is a growing recognition that Lord Falconer, who has appealed to judges to jail fewer people and make greater use of bail, might be forced to take drastic action to cut the prison population. He could approve the "executive release" of thousands of inmates nearing the end of their sentences, a "nuclear option" last used in the 1980s.

Lord Falconer could extend the home-detention curfew scheme, under which offenders are released on electronic tags up to four and a half months before the end of their sentence. Alternatively, he could allow the 1,500 to 2,000 offenders allowed out for part of the day on temporary licences to stay out around the clock.

The problem is that all options open to him are politically unpalatable, particularly as Labour and the Tories often appear to be competing to sound more hardline than the other on law and order.

What has caused the rise in the prison population?

The number behind bars has been increasing steadily since the 1950s, apart from a fall between 1986 and 1991. The respite was short-lived, with many criminologists believing the coincidence of two events in the early 1990s sent the prison population rocketing.

First, the murder of Merseyside toddler James Bulger in 1993 by two 10-year-old boys caused a nationwide sense of revulsion and a growing feeling that society was threatened by violent criminality.

Second, the hardline Tory Home Secretary Michael Howard was at the time faced in the Commons by a rising Labour star, Tony Blair, determined to cast off his party's reputation for being soft on law and order.

The issue, which used to barely feature in election campaigns, has been at the heart of political combat ever since. It is inevitable that there has been a knock-on effect on the number of people jailed by courts and on the length of their sentences.

England and Wales now tops the western European prison population league table. Rob Allen, director of the International Centre for Prison Studies in London, does not think that means this country's citizens are inherently more recidivist than their European neighbours.

He said: "We tend to use the criminal justice system to deal with problematic people - we take them through the courts rather than drug treatment programmes or mental health provision. Other countries tend to use the criminal law as a last resort, rather than a way of mopping up social casualties."

Critics also point to the flurry of criminal justice legislation under this government, which has created more than 3,000 offences in the past decade, as a another key reason for the emergency.

What is the impact on prison conditions?

The pressure on the system was symbolised recently when a dilapidated wing of Norwich Prison with 150 spaces had to be reopened days after it was closed for refurbishment. More inmates are sharing two or three to a cell, which prison governors warn can stoke up tensions. Rehabilitation work is undermined as inmates are bussed around the country, which means they are further from their families and find their educational courses are disrupted.

Sinead Hanks, a development officer with SmartJustice, says: "Things are getting a lot worse because you have a lot of people with problems crammed into one place. It is a cycle that builds upon itself and affects the prison workforce as well."

There are some causes for optimism. Extra vigilance has managed to reduce the suicide rate among inmates; nor has there been a major prison riot for years. The nightmare for ministers is that rising tensions and soaring temperatures this summer could prove a combustible mixture.

What alternatives are there to jail?

Diverting from prison some of the 50,000 people a year who receive sentences of less than 12 months would end the crisis overnight. Ministers are trying to encourage the courts to impose fines rather than prison sentences. The stumbling block is that falling collection rates havedamaged their credibility, a problem the Government has tackled with mixed success.

Courts are also wary of the effectiveness of community sentences. Most in the probation service believe they cut reoffending, but the statistics are ambiguous.

A new approach could be taken to the treatment of mentally ill offenders, with Primary Care Trusts required to provide alternative treatment for them. Women-only bail hostels could be developed for female offenders - the vast majority of whom are jailed for petty crime - enabling mothers to keep in touch with their children. They could get help with drugs, drink and money problems without breaking up families.

Are too many people jailed?

Yes...

* Many of those currently behind bars could be rehabilitated in the community

* Tensions are rising in prisons because of overcrowding, creating a danger of rioting

* Non-violent offenders on short sentences pick up criminal skills inside

No...

* Keeping offenders out of circulation protects the public and cuts crime

* Violent crime is rising fast - there must be a powerful and effective deterrent

* The public has little confidence in community sentences, and does not see them as a serious punishment