Just months after pedophilia allegations rocked South Australian politics, a former Liberal minister and candidate for a vital state marginal seat is at the centre of a storm over a same-sex relationship.

“Mark Brindal is the Liberal MP who claims to have been blackmailed over his sexual relationship with a 24-year-old man,” The Adelaide Advertiser reports today. “The married father of four had a three-month affair with the man – who has a mental incapacity – earlier this year,” the paper claims. “The pair had sex in Mr Brindal's Unley electorate office several times."

“Mr Brindal, 57, told his wife Pam and four adult children he was bisexual after his ex-lover's foster carer allegedly demanded money in return for not going public.” Yesterday's Adelaide Sunday Mailreported that police were investigating allegations by an unnamed MP that he was the victim of a blackmail attempt. “It is believed [SA Liberal Leader] Mr Kerin was interviewed by members of the anti-corruption branch on Friday.”

Brindal told The Advertiser yesterday he couldn't speak publicly as he was “under special instructions from police not to say anything.” However, he spoke frankly at a forum in Adelaide yesterday on same-sex marriage. “Mr Brindal entered a relationship with a 24-year-old pensioner under the protection of the Guardianship Board in March,” The Advertiser reports. “The man, who lives in supported accommodation in the western suburbs, has a ‘mental incapacity' and his financial affairs are administered by the Public Trustee.”

No breach of the law appears to have occurred, but it is where the story may lead that's causing consternation. Earlier this year, Brindal announced he wouldn't seek preselection in his seat of Unley, stacked over several years. Instead, he announced he would contest the vital Labor marginal of Adelaide. Adelaide is one of two vital suburban seats the Liberal Party needs to win to retain government in South Australia at next March's election.

Party heavies breathed a sigh of relief when Brindal bowed to the inevitable and avoided a messy preselection fight in Unley – and welcomed his candidacy in Adelaide, where the first term Labor MP, former city Lord Mayor Jane Lomax-Smith has disappointed many. They were finding it hard to get a decent candidate. At the moment the South Australian Liberals are saying they still expect Brindal to contest the seat – but anything could happen now.