A South Australian MP who has consistently championed gay rights has withdrawn as a Liberal candidate from upcoming state elections after admitting to a same-sex affair, in a move queer activists say could rob them of a key parliamentary ally.

Mark Brindal announced on Tuesday he would not stand as a Liberal candidate in state elections next March, after admitting he had a three-month affair with a 24-year-old man earlier this year.

I believe that this decision reflects particularly the needs of my family and the interests of the Liberal party as it prepares for the next election, Brindal said in a statement on his website.

The affair -“ which included sex at Brindal’s electorate office -“ came to light after the 24-year-old’s foster father approached Brindal and SA Liberal leader Rob Kerin in June and allegedly demanded money, The Australian reported.

Police are now investigating the blackmail claims against the 24-year-old and his foster father.

Brindal, who is married, admitted the sex in his electorate office had been inappropriate.

But he said he would not have regretted the affair if it had not been made public, and accused homophobic members of the Liberal party of pushing for his departure.

Some members in the Liberal party pushed me by exhibiting their extraordinary 1950s neanderthal intelligence, Brindal was quoted as saying by the Herald Sun.

They made judgments on a couple of [media] articles and said, -˜This is too much, we can’t have this guy as a candidate.’

Brindal said he would expose other MPs’ hypocrisy in his remaining months in parliament.

If my personal life has been fair game, I really don’t see why anybody else’s shouldn’t be, he said.

That includes serial womanising, drinking, gambling, debts -“ many, many things.

Brindal has not ruled out standing as an independent at the next South Australian elections.

However, his departure from the Liberal ticket is a setback for South Australia’s gay law reform process, according to state activist Matthew Loader.

Loader, spokesperson for South Australian gay rights lobby group Let’s Get Equal, told Sydney Star Observer Brindal had been a prominent advocate for queer rights during his 16 years in parliament.

In very simple terms, South Australia will lose a very good parliamentary advocate, someone who has been consistently strong [on] and committed to gay rights legislation, Loader said.

We lose out [because] we need strong advocates across all parties, and Mark was a particularly notable one in the Liberal party in South Australia, Loader said.

Earlier this year, Brindal put forward a private member’s bill proposing civil unions for people in non-traditional relationships, including same-sex couples.

Brindal’s move put pressure on South Australia’s Labor government to expedite its own same-sex rights bill, which was proposed last year but is yet to become law, Loader said.

You could say he [Brindal] introduced his bill knowing that the government had its bill there. It was partially a way of putting pressure to get the government bill passed, he said.

It also put the issue of registration [of] civil unions well and truly on the state parliament’s agenda.

South Australia is the only state or territory whose laws do not recognise same-sex partners.

South Australian Liberal leader Rob Kerin said Brindal has paid a significant price for what he concedes was a serious error of judgment, but lauded the MP’s overall contribution.

It takes courage to stand up and be counted as he has done and I don’t believe his contribution to South Australian politics over the past 16 years should be diminished by his actions of the past few months, Kerin said.

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