The Girl Guides will allow boys who identify as female to shower with girls, it has emerged.

For the first time, Girlguiding's official guidance instructs guide leaders to allow members who were born male but now identify as female to share changing rooms, toilets and sleeping quarters with girls when away on excursions.

The 107-year-old organisation updated its rules, which apply to members aged from five to 25, to allow transgender girls to "share accommodation with other young members if they wish" and use the same facilities.

Guidance on transgender members was first added in 2015 and updated this year.

The new guidance, issued on the group's UK website, says that "the use of gendered facilities," including showers, toilets and changing rooms, "can cause anxiety".

It adds: "Members are allowed to use the facilities of the gender they self-identify as."

Julie Bentley is the chief executive of the Girl Guide Association credit: Andrew Crowley

Julie Bentley, Girlguiding Chief Executive, said that the organisation follows the requirements set out in the Equality Act 2010, which states that organisations providing single-sex services must treat people according to their acquired gender.

Ms Bentley said: "In line with our values of inclusion, we welcome any young person who self-identifies as a girl or young woman.

“If a young person doesn’t feel comfortable sharing accommodation, for whatever reason, we encourage them to talk to their leader about alternative accommodation and facilities."

The Government announced in July that it was to allow adults to legally challenge their gender without facing "demeaning" rules that force people to undergo a formal medical diagnosis.

There are concerns, however, that sharing accommodation and personal facilities will threaten the safety and privacy of girls, especially as parents of younger members would not be automatically told if their daughter was sharing such facilities.

The guidance states that it is not "best practice" to inform parents that a trans person will be attending a residential event.

David Davies, Conservative MP for Monmouth in South Wales, told The Mail on Sunday: "If transgender girls who are physically male are going to be sharing facilities, it’s going to make some girls threatened and uncomfortable and the Guides shouldn’t be doing that."

In the Guide's "Girls' Attitudes Survey" published earlier this year, members' make several references to having girl-only safe spaces. One respondent said: "Being the only female in a male-dominated environment can be very difficult, so it’s important to make sure that girls feel welcome and safe in these places."

The report states that the organisation offers "girls a place where they can really be themselves with other girls and share the experience of growing up as a girl in today’s world."

The organisation's gender guidelines state: "'Girl' is based on gender identity. This means that any child who self-identifies as a girl should feel safe and welcome in our girl-only space regardless of the sex that they were assigned at birth."

It is not know how many transgender members are in the guides.