One of the Scottish Greens’ most prominent MSPs has resigned from the party, citing tension around transgender rights.

Andy Wightman announced on Friday that he is leaving the party after more than 10 years as he claimed there is intolerant dialogue within it on “questions of sex and gender”.

The party, whose Holyrood group has now decreased to five MSPs, said it is “deeply disappointed” by Mr Wightman’s resignation.

Put simply, I cannot operate in this kind of environment

In a letter to the party’s co-leaders Lorna Slater and Patrick Harvie, Mr Wightman said he will continue to “support Green politics” despite leaving the party.

The Lothians MSP said he feared expulsion from the party due to his support of an amendment to a Bill passed at Holyrood last week.

The Greens and the Liberal Democrats opposed an amendment from MSP Johann Lamont to the Forensic Medical Services Bill.

The amendment sought to allow victims of sex crimes to be able to choose the sex, rather than the gender, of the person who examines them afterwards.

Mr Wightman said he had been minded to support the move but faced strong opposition from within his party.

In his letter, he wrote: “For some time now, since I was admonished for attending a public meeting at Edinburgh University in June 2019, I have been saddened by the intolerance shown by some party members to an open and mature dialogue about the tensions and conflicts around questions of sex and gender in the context of transgender rights and women’s rights.”

He went on to say he had been threatened with “possible suspension, deselection or expulsion” if he voted in favour of Ms Lamont’s amendment.

He continued: “I understand that the Scottish Green Party has a strong commitment to equalities and trans rights.

“However, some of the language, approaches and postures of the party and its spokespeople have been provocative, alienating and confrontational for many women and men.

“It has become evident to me that the sort of open-minded public engagement I would like to see take place on this topic is incompatible with a party that has become very censorious of any deviation from an agreed line.

“Put simply, I cannot operate in this kind of environment and Thursday’s vote and the discussions that took place around it were the final confirmation of that.”

Mr Wightman said he will continue to work constructively with Green MSPs ahead of next year’s Holyrood election.

Responding to his resignation, a spokesman for the party said: “The Scottish Greens are focused on building a greener and fairer Scotland that tackles the climate emergency, so Andy Wightman’s decision not to be part of our movement anymore is a matter of deep disappointment.

“Land reform, empowering local democracy and community empowerment are core Green issues, and Andy’s contribution has been very important, but the Greens remain committed to carrying on this agenda without him.

“The Scottish Greens wish Andy well in whatever he decides to do next.”