Caroline Farrow, a speaker on gender and sexuality from Catholic Voices, told Premier's News Hour: "There is a biological reality and there is a biological component there that we can't just reject."
She was speaking after the Women and Equalities Committee said that Britain has "a long way to go" to ensure equality for transgender people, in its first report on the issue produced by a UK parliamentary committee.
Transgender describes someone who identifies as a different sex to the physical body they were born in, and the report calls on the Government to produce a new strategy for full transgender equality within six months.
The Women and Equalities Committee estimated that as many as 650,000 people in the UK are "gender incongruent to some degree" and said it was believed that around one third of transgender adults and half of young people attempt suicide.
Caroline Farrow said: "My young children can't make up their mind what they want for lunch, or what they want for Christmas, let alone a big momentous decision 'Mummy I'm not really a girl, I'm a boy', and you wonder quite how much of this is being projected and imposed on children."
She told Premier that society is being told that "gender is fluid, gender is just what you think it is.
"It's quite dangerous I think to say identity is just what I say it is, or what you say it is then actually other groups like the government can just appropriate that and say your identity is what I say it is."
Other recommendations in the report include the introduction of the option to record gender as 'X' in a passport, and removal of the requirement to show a doctor's letter to alter the gender shown.
Listen to Premier's Marcus Jones speak to Caroline Farrow here: