Urgent action is needed to address poor practice in the treatment of women and girls on their period in police custody, the Government has been warned.
A watchdog suggested conditions for menstruating detainees may breach human rights laws and called on Home Secretary Amber Rudd to launch a review.
The Independent Custody Visiting Association (ICVA) said it observed one woman in a police cell dressed in a paper suit.
A request for her to be given underwear so she could have some sanitary protection was refused, according to the ICVA.
It said: "Inspection reports suggest that this is not an isolated incident and that there is poor practice in forces across England and Wales in the treatment of women and girls experiencing their period in the cells".
The assessment flagged up a number of shortcomings.
It said few forces appear to consistently apply guidance which requires women detainees be offered a hygiene pack without asking, little privacy is offered for the changing of sanitary protection and hygienic facilities for washing are not always made available.
Katie Kempen, chief executive of the ICVA, said: "Dignity in the cells must mean dignity for all.
"No woman or girl should be left bleeding in a cell in indignity simply for want of a difficult conversation or an inexpensive box of tampons."
The organisation flagged up a legal opinion which it said concludes that a failure to ensure access to safe and adequate sanitary protection in police stations is likely to breach human rights standards.
It has written to Ms Rudd calling for swift action to protect the dignity of women and girls having their periods in police custody.
The body, which is funded by the Home Office, called for a review of existing practice and revisions to statutory codes of practice to include clear guidance on the treatment of menstruating women in police custody.
Dame Vera Baird, Police and Crime Commissioner for Northumbria, backed calls for action.
She said: "Failure by police to give good quality sanitary protection packages automatically to all female detainees is lamentable."
National Police Chiefs' Council (NPCC) lead for custody Assistant Chief Constable Nev Kemp said:"The police service is committed to upholding the highest custody standards to ensure that all detainees are treated in the right and proper way.
"Although there have only been a very small number of detainees affected by inadequate sanitary protection, we are committed to achieving greater consistency across the country so that women in custody are always treated with dignity and respect.
"In consultation with women's groups and other organisations, we are in the process of developing comprehensive guidance for officers on how to deal with these sensitive and often complex cases."
The Home Office said it was working closely with the ICVA and NPCC "to understand where improvements can be made on this issue."