One in 50 male offenders in prisons say they are transgender, according to a survey by the Inspectorate of Prisons.
The report comes amid concerns inmates may be trying to gain advantages, or be placed in all-female prisons in order to have access to women.
Prisoners who say they are transgender can have seperate showers, single cells, and can apply to switch between male and female prisons.
The annual report by the Chief Inspector of Prisons, Peter Clarke, suggested there are up to 1,500 trans inmates in England and Wales, more than ten times the previous estimate.
Clarke said: “Sometimes we find the numbers of people identifying as transgender are higher in our survey than the prison will think.”
He added that inspectors had seen “considerable care” shown to transgender prisoners.
Chair of the Prison Officers Association Mark Fairhurst said there “would always be some trying to abuse the system”.
Harry Fletcher, Director of the Victims’ Rights Campaign, said that “for some this is a total try-on”.
Last year, a transgender prisoner who sexually assaulted two women while in an all-female prison was sentenced to life.
The man, known as Karen White, had been placed in a women’s jail because he had told prison authorities he ‘identified as a woman’.
The prison service apologised for the mistakes which had been made in allowing White, who had previously been convicted of a sex attack on a child, to be assigned to an all-female jail.
A spokesman said: “While we work to manage all prisoners, including those who are transgender, sensitively and in line with the law, we are clear that the safety of all prisoners must be our absolute priority.”