Asked for his definition of a woman, he told Talk TV’s Peirs Morgan: ‘Of course, I know what a woman is, an adult human female.’
Morgan went on to quiz the PM about ‘trans woman athletes demolishing women, female athletes’ and his feelings about that.
Mr Sunak said: ‘Well, I think that doesn’t strike most people as being fair, right? So that’s why when it comes to these questions, biological sex matters.
‘Now that, you know, we can and will have compassion and tolerance and understanding for everybody who is thinking about transitioning and changing their identity or gender.
‘But you know, for me, when it comes to whether it’s sex, whether it’s women’s spaces, whether it’s prisons, biological sex really matters.’
The Government found itself facing off against Scottish First Minister Nicola Sturgeon after vowing to prevent gender recognition reforms passed by Holyrood from going forward for royal assent.
The issue exploded following the case of Isla Bryson – who was convicted of raping two women while she was a man called Adam Graham.
Bryson was initially taken to Cornton Vale prison near Stirling – Scotland’s only all-female jail – after being convicted, before being moved to the male estate following public outcry.
Ms Sturgeon has since been accused of undermining her own laws by suggesting Bryson is not truly transgender.
Scottish Conservative leader Douglas Ross used First Minister’s Questions on Thursday to try and corner Ms Sturgeon on her belief in self-ID – the process by which a trans person does not require a medical diagnosis to identify as a gender different to that of their birth sex.
Ms Sturgeon said: ‘This individual claims to be a woman – what I said was that I don’t have information about whether those claims have validity or not.
‘But I don’t think Douglas Ross and I are disagreeing here, because what I think is relevant in this case is not whether the individual is a man or claims to be a woman or is trans, what is relevant is that the individual is a rapist.
‘That is how the individual should be described, and it is that that should be the main consideration in deciding how the individual is dealt with – that is why the individual is in a male prison, not in the female prison, these are the issues that matter.’
MSPs passed the Gender Recognition Reform (Scotland) Bill in Holyrood before the new year, but it was later blocked from becoming law by Scottish Secretary Alister Jack using an unprecedented Section 35 order.