Transgender people who agree with using the biological terms “male” and “female” are afraid to speak out because of the backlash they will receive on social media, a tribunal has heard.

Kristina Jayne Harrison, a 54-year-old transgender woman who was born a man, told an employment tribunal that attempts to characterise the traditional terms of men and women as “offensive” by lobby groups are not supported by all transgender people.

Ms Harrison was giving evidence in support of Maya Forstater, a 46-year-old tax expert who is suing her former employer, the US think tank Centre for Global Development (CGD), for dismissing her after she tweeted that “male people are not women”.

Her sacking has led to an unprecedented legal case, which could see the view that a person cannot biologically change their sex - known as ‘gender critical' - become a protected philosophical belief under the Equality Act 2010.

Lawyers representing CGD cited a “glossary of terms” by a pro-transgender charity, which defines the terms biologically male and female as “problematic phrases” because “a person's sex is determined by a number of factors - not simply genetics.”