Caleb Orozco has been denounced as the antichrist, received death threats and had a beer bottle smashed into his face. Next Tuesday, the gay rights campaigner will face a very different kind of challenge, when he comes up against the attorney general of Belize and the leaders of the country's churches.

The courtroom battle over the Caribbean state's colonial-era "anti-buggery" laws is a significant milestone in a global campaign to decriminalise homosexuality.

For four days, Orozco, supported by the former UK attorney general Lord Goldsmith and Godfrey Smith, Belize's former attorney general, will dispute the legality of a 19th-century law drafted in Britain. Defending section 53 of Belize's criminal code, which outlaws "carnal intercourse" between consenting same-sex adults, will be Belize's current attorney general, Wilfred Elrington, backed by the country's Catholic, Anglican and evangelical churches.

Belize's churches have been at the forefront of those condemning the legal challenge. The most outspoken opponent is Pastor Scott Stirm, a Texas evangelical missionary who runs Belize Action; he has praised the existing legislation as "a good law that protects human dignity" on the grounds that it is often used in sex abuse cases.

Section 53 declares that "every person who has carnal intercourse against the order of nature with any person or animal shall be liable to imprisonment for 10 years". Like so many laws around the world criminalising homosexuality, Section 53 is a legacy of imperial rule from London. Buggery with consent and bestiality were deemed merely to be "public nuisances" when the criminal code of Belize came into force in 1888. The offence was re-categorised as an "unnatural crime" during the second world war.

The case, to be heard in Belize's supreme court, is also supported by the UK-based Human Dignity Trust, which has recruited Goldsmith to help present the claim. He will argue that section 53 is inconsistent with the country's constitution and in breach of international standards. The trust is supporting legal actions around the world to remove laws that criminalise gay relationships. Cases have also begun in Jamaica and northern Cyprus, both formerly British colonies.

Orozco, 39, president of the United Belize Advocacy Movement, is openly gay. "I don't have a partner now," he told the Guardian from Belize City. "If the law is changed and people are less scared, I might have a personal life.

"The loudest homophobes are the evangelicals. People have called me the antichrist for taking this case. Extreme homophobes I can tolerate but people I have known for years, who I did not think would take such a position, that's hurtful."

One message on a Facebook site debating his case, which he believes amounted to a death threat, referred to a passage in Leviticus that prescribes the death penalty for any man who has sexual relations with another man. Another threat suggested adjourning the case until Orozco died of a "cause due to sexual preference".

In February 2012, Orozco was taunted with anti-gay insults and hit in the face with a bottle. He needed surgery. "They took it upon themselves to teach me a lesson," he recalled. "They pretended they had nothing in their hands ... It was a humiliation. I had fought for over two decades to stop assaults. That one caught me."

Section 53, he said, has been used, though not frequently, to prosecute those involved in consenting gay relationships. Its presence ensures that being gay remains taboo and that there is a climate of hatred.

"I know of a case where [people] blackmailed a man for $400, saying that otherwise they would tell his parents [about his sexuality]. Our opponents say we are trying to introduce gay marriage but this law has nothing to do with gay marriage."

Belize Action has distributed leaflets claiming that Section 53 has "never been used to charge, prosecute or convict any person for a consensual act". Another flyer declares: "[UniBAM] are bringing foreign attorneys from foreign homosexual organisations with huge foreign funding to impose their foreign values upon [us]."

Belize, with a population of 330,000, achieved independence from Britain in 1981. The stance of its Anglican and Catholic churches is at odds with positions taken by the Church of England and the Vatican on gay rights.

A statement released by the Roman Catholic Bishop Dorick Wright of the diocese of Belize and Belmopan, Bishop Philip Wright of the Anglican diocese of Belize and Rev Eugene Crawford of the Belize Association of Evangelical Churches announced in 2011 that they were joining the government side in the test case.

It declared: "This lawsuit was filed to establish a new 'right' to engage in homosexual acts in Belize. In every country that has granted a new 'right' to homosexual behaviour, activists have promoted and steadily expanded this 'right' to trump universally recognised rights to religious freedom and expression."

Jonathan Cooper, chief executive of the Human Dignity Trust, said: "This case is a microcosm of what's going on around the world. People are working through the courts. [Orozco] is a really brave gay who is taking on the full wrath of the Christian right."

Orozco's case could eventually end up before the Caribbean's highest court of appeal, based in Trinidad and Tobago. If the case reaches Belize's court of appeal – one rung above its supreme court – the next step would be to seek permission to appeal to the Caribbean court of justice (CCJ). Belize has been a member of the CCJ since leaving the jurisdiction of the London-based privy council in 2010.

The court has not heard a gay rights case since opening in 2005, although an application is being prepared by Maurice Tomlinson, a Jamaican activist for the lesbian, gay, bisexual, and transgender community, challenging Belize's immigration laws, which bans gay men and women from entering the country.