Out actor Sir Ian McKellen has backed a proposed bill that would allow gay and lesbian couples to marry in Northern Ireland.

It is the fifth attempt at marriage equality in Northern Ireland, the sole part of the UK where gay couples are excluded from civil marriage.

“As a gay Englishman, whose ancestors hail from County Antrim, I am concerned that the Northern Ireland Assembly should establish full legal equality for LGBT residents in Northern Ireland,” McKellen wrote.

“Northern Irish people should not be the victims at home of specious arguments in favour of inequality. They should not have to travel to Britain nor to the Republic, to be treated equally.”

“Just as coming out as a gay person, changes one’s life entirely for the better, coming out as a country, in favour of equality, will bring credit to the entire citizenry, regardless of their sexuality or gender.”

“I hope the vote will give us all a chance to celebrate the unity of civil rights already enjoyed by LGBT people in adjacent countries,” he added.

While the proposal is expected to narrowly clear the region's parliament, the Democratic Unionists (DUP), the largest party in the Stormont assembly, has threatened to torpedo the legislation with a “petition of concern,” which blocks bills not widely supported by leading parties.