There has been a significant increase in the number of prisoners who have killed themselves in jails in England and Wales, figures show.
There have been 50 suicides by prisoners so far this year
So far this year, there have been 50 inmate suicides, compared with 35 in the first half of last year, says the Prison Service.
Chief Inspector of Prisons Anne Owers linked the sharp rise in suicides to prison overcrowding.
The Prison Service said its efforts to prevent suicides were "unprecedented".
Out of the 50 inmates to have killed themselves to date this year, 17 had been on remand awaiting sentencing and six were women, according to the Prison Reform Trust.
Sixty-seven inmates killed themselves in the whole of 2006.
If 2007's deaths continue at the same rate, it would reverse a trend which has seen prison suicides fall from 95 in 2004.
Ms Owers told BBC Radio 4's Today that the overcrowding crisis had seen prisoners housed in police and courthouse cells, which means they do not have access to the support offered in proper jails.
She said: "Inevitably, while prisons are operating under the pressures they are, staff are under stress, prisoners are under stress, and that means the most vulnerable won't always be able to get the support they need."
The prison population hit a record of 81,040 in June, before dipping by 1,500 earlier this month because of the government's early release scheme.
It means no offenders are being held in overspill cells in police stations or courts for the first time since April.
The Prison Reform Trust says the pinch of overcrowding is being felt most acutely in women's prisons and in the "traumatic" first few days of custody.
A spokesman said: "Women's prisons are being closed and reopened as men's. The female inmates are being ripped away from areas they know well and moved around the country.
"And we know from study after study that one of the real pressure points where people are most likely to be distraught, self-harm, or try to commit suicide is in the first few days of custody and that's the period that has been most disrupted by overcrowding."
The Prison Service said it had worked to make jails safer for the "high proportion of very vulnerable adults" in the prison population, and as a result, the number of inmates who killed themselves fell to 67 last year - the lowest level since 1997.
It said staff training and procedures had been improved.
A spokeswoman added: "In the face of rising population levels, suicide prevention efforts are proceeding with unprecedented energy and commitment."