Too many women are being jailed for petty offences, the prime minister's wife, Cherie Blair, has said.
Mrs Blair was speaking under her professional name
Many of those held in prison were suffering from mental health problems and had been victims of sexual abuse and domestic violence, Mrs Blair said.
Prison would "never be the best place" for such women to rebuild their lives, she wrote in The Observer under her professional name, Cherie Booth, QC.
Figures show the number of women in jail has risen 173% in the past decade.
Most of that rapid rise has been during Tony Blair's administration.
Mrs Blair acknowledged that women cannot expect to be treated with "kid gloves" and female offenders must be punished for their crimes.
But she said that prison should be treated as "the absolute last resort for women whose offending is so serious that there can be no alternative to
custody", adding: "I'm not sure that is always the case."
"Our prisons are full of distressed women who, rather than being career criminals or a danger to anyone but themselves, are inside because they have made some terrible mistakes or choices in their lives."
Mrs Blair voiced support for government initiatives to develop punishments in the community, electronic tagging and drink or drug treatment.
'Horrifying' suicide numbers
She also welcomed this week's conference of the Fawcett Society, a campaign group to promote equality for women.
A MORI survey conducted for the society showed on Sunday that the public favoured treatment for many female offenders above prison sentences.
In the survey 82% of people favoured greater provision of mental health treatment centres, 74% supported residential treatment for drug addicts and 68% said community sentences could be an alternative to prison terms.
The MP, Vera Baird, QC, who is chair of the society's commission on women and criminal justice system, spoke ahead of her findings which are being released on Wednesday.
"The dramatic increase in the number of women in prison has put a severe strain on the Prison Service," she said.
"The horrifying number of suicides indicates the level of desperation amongst women prisoners."