Foreign women are being imprisoned for crimes they were forced into, after being trafficked or coerced into offending, campaigners have said.
One in seven of all women behind bars in England and Wales are foreigners, serving sentences crimes involving drugs or immigration offences, the Prison Reform Trust said.
Often their crimes are non-violent and these foreign women need to be identified sooner as victims of exploitation. The reform calls for changes to the system as at the moment assessing their status is left until after the women have pleaded guilty.
One African woman, whose son was kidnapped, needed money to pay legal fees to ensure his return. She was jailed for six-and-a-half years after she tried to smuggle five kilograms (11lbs) of cocaine into the UK.
The woman, quoted in the report, said: "I was scared, at that point, I have a baby... At that time we have no money, nowhere to live... I was with my son. I have to do this, it was a pressure. Big pressure on me. That person come to me and say (sic) 'look I got a lot of money', ridiculous amount..."
A joint report by the Prison Reform trust and Hibiscus, which works with women in prisons, showed almost half (46%) of foreign prisoners were in jail over drugs, compared with one in five (21%) of the UK population.
It also showed that while the number of women in jail had risen by 27% over the last 10 years, the number of foreign women behind bars rose 49%.
And the number of women entering the justice system from Eastern Europe now made up a fifth of all new cases, while one in eight came from China or Vietnam, figures from the Hibiscus caseload showed.
The report called for sentencing guidelines for drug couriers to "take account of the role that women play in this offence" and to ensure that any evidence of coercion, exploitation and duress is "integral to all sentencing decisions".
Olga Heaven, director of Hibiscus, said: "High numbers of women are brought into the UK deceived and exploited.
"Many are young women with a dream of going to a first world country to achieve something, but what they are brought in for is either prostitution or some other kind of enforced labour.
"Others who have been provided with false documents are detained by immigration or custom officials and often find themselves imprisoned on arrival.
"More needs to be done to identify vulnerable foreign national women in need of protection before they get into trouble with the law."
Women arrested over passport offences trying to leave the UK should be allowed travel to their country of origin, said the report.
They should not to necessarily be charged with a criminal offence, if they pose no threat to UK security.
Juliet Lyon, director of the Prison Reform Trust, added: "Far too many foreign national women are languishing in British jails having been coerced or trafficked into offending.
"There are ways out of this mess but only if the Government is prepared to redouble its efforts to catch the traffickers, who profit from their grubby trade, rather than allowing the burden of punishment to fall on vulnerable women - many of whom have been victims as well as perpetrators of crime."
Immigration Minister Damian Green has said that human trafficking is "a brutal form of organised crime" and "combating trafficking and looking after its victims is a priority" for the Government.
"Having any number of people trafficked into the UK is unacceptable," he said.
A Government spokeswoman said: "Human trafficking is a brutal form of organised crime where people are treated as commodities and exploited for criminal gain.
"The Government is committing to tacking this, which will be helped by the proposed National Crime Agency.
"People identified as victims of trafficking while already in detention are likely to be released to allow them to access the necessary support.
"However, not all individuals identify themselves as victims when they first encounter authorities, which can lead to them being detained for a period.
"Where custody is appropriate, we are committed to meeting the complex needs of women offenders and recognise their often long histories of abuse, mental health issues and substance misuse problems."