A trans woman who had gender reassignment at the age of 72 says the UK Supreme Court’s ruling over the definition of a woman will have “dire consequences” for the safety of trans people.

Campaigner Kerrie Meyer, from Shetland, said it would allow “bigotry, transphobia, assault and untold life threatening dangers to escalate”.

On Wednesday, judges unanimously ruled that a woman is defined by biological sex under equalities law.

It marked the culmination of a long-running legal battle which could have major implications for how sex-based rights apply in Scotland, England and Wales.

The Scottish government had argued that transgender people with a gender recognition certificate (GRC) are entitled to the same sex-based protections as biological women.

But judges sided with campaign group For Women Scotland, which brought a case against arguing that sex-based protections should only apply to those born female.

Campaigner Kerrie, founder of the Shetland Islands’ Pride festival, criticised the ruling and said it would set back progress for trans people like her.

She said: “At the stroke of pen, the security and well-being of all transgender people, whether now deemed as biological male and female, is in jeopardy.

“The Supreme Court’s ruling has created severe implications for all trans people and has failed to take into account the dire consequences and untenable results that will occur.”

Kerrie, now 77, moved to Shetland from Hastings in East Sussex in 2008.

She said the rights of trans people had been advanced by the Gender Recognition Act 2004 and the Equality Act 2010.

She believes the Supreme Court case was motivated by “reserving and maintaining” woman’s spaces from trans women, regardless of whether they held a Gender Recognition Certificate.

The Supreme Court had been asked to decide on the proper interpretation of the 2010 Equality Act, which applies across Britain.

Judge Lord Hodge said the ruling should not be seen as a triumph of one side over the other, and stressed that the law still gives protection against discrimination to transgender people.

Kerrie told BBC Radio Scotland that it would be “totally and utterly ridiculous” for her to change her behaviour in public.

She said: “I was born a man. Under the law I am a woman. I dress like a woman. I act like a woman. And I am a woman.

“If I go to the toilet and there is another woman in there, they don’t know whether I have got a gender recognition certificate or not.”

Kerrie also believes that recognition certificates should only be granted if someone has undergone gender reassignment surgery.

Campaigners who brought the case against the Scottish government hugged each other outside the Supreme Court after the ruling was made on Wednesday.

First Minister John Swinney said the Scottish government accepted the judgement.

He said: “The ruling gives clarity between two relevant pieces of legislation passed at Westminster.

“We will now engage on the implications of the ruling.”

The Scottish government said ministers had acted “in good faith” during the legal proceedings.

It noted that the Equality and Human Rights Commission was updating its guidance in response to the judgement.

The UK government said the ruling would bring “clarity and confidence for women and service providers such as hospitals, refuges, and sports clubs”.

“Single-sex spaces are protected in law and will always be protected by this government,” a spokesman added.