The Green Party’s Dr Rupert Read has “unreservedly” apologised for a series of tweets in which he appeared to question the validity of trans people’s gender.

He had posted that the use of the word “cisgender” as the opposite of “transgender” troubled him.

The “cis” prefix is frequently preferred by transgender campaigners over terms such as “biological” or “genetic”.

He also shared a blog post written by him in January 2013, in which he defended feminist writers who had been accused of transphobia.

The philosopher and parliamentary candidate for Cambridge described trans women as “a sort of ‘opt-in’ version of what it is to be a woman”.

“Imagine that some people regard themselves within themselves as disabled, as missing a limb,” he wrote, suggesting that people should not be “forced” to recognise transwomen as women. “Are disabled people obliged to regard those people as already part of the disabled community?” he continued. “I would suggest: obviously not.”

Dr Read faced fierce opposition from transgender activists and feminists on Twitter.

Sarah Brown, former Cambridge councilor and trans activist, told Cambridge News: “Rupert seems to be endorsing a fringe form of feminism that portrays transgender women as dangerous sex pests and predators.”

He has since expressed his regret on the social media platform:

Responding to Brown’s remarks, Read added: “It is completely, 100 per cent untrue, for instance to claim that I ‘portray transgender women as dangerous sex pests and predators’. On the contrary, I reject transphobia completely.

“But I also remain a very strong backer of feminism. All that I have done is join many feminists in saying that it is up to women, not anyone else – and certainly not me – to decide who gets let into women-only spaces, such as women’s toilets. All women have a right to be involved in making those decisions.”

“I am listening to what those who have been upset by or who disagree with my views on this are saying, and I hope to learn from the whole affair. The first lesson I am learning is: I’m not going to even try talking about these things on Twitter anymore.”

Dr Read has since issued another clarification to The Independent on his comments.

“The tweet that was at the root of this chain of events, a tweet I wrote about the term 'cis', has been over-interpreted,” he said. “I am not 'against' the word 'cis', or 'cisgender' – I employ it myself sometimes. So it certainly does not trouble me that others use it! And I certainly do not think it is OK (say) for cis women to speak of themselves as ‘real women' or anything like that, because that would implicitly suggest, wrongly, that trans women are not. Whereas: I most certainly do not and never have believed that trans women are not real women, or are any less women.

“Moreover, I do not and never have believed that being a trans woman manifests an 'opt-in’' idea of what it is to be a woman. I invented the phrase only to discuss a hypothetical philosophical position that I was arguing against. I never applied it to trans women – because I certainly do not believe it applies to trans-women, because trans-women typically do not experience their gender-identity as a choice – an opt-ion – at all.