A man who poured petrol around former premier Mike Rann's Adelaide electorate office and threatened to light it has apologised in court for distressing the staff.

Mark Anthony Lock, 49, went to the office at Salisbury last May and doused himself and the floor with petrol.

He had a cigarette lighter with him.

Lock pleaded guilty to an aggravated count of threatening to damage property by fire.

He was considering changing his plea and arguing he was mentally unwell at the time, but the District Court was told a mental health defence could not be considered

Defence lawyer Andrew English said Lock had a long history of alcoholism and problems managing emotional stress.

He said it caused impulsive behaviour and had resulted in convictions for similar offending at Berri and in Tasmania.

Mr English said Lock had been angry with the South Australian Government, accusing it of not listening to the people and wasting taxpayers' money.

The court was told Lock became obsessed with media coverage of criticism of the Government.

Glass trigger

It heard the electoral office incident was triggered when a glazier told Lock that sheets of glass intended for the former premier's office had been rejected for being the wrong colour and would be discarded.

Mr English said Lock became dramatically obsessed with the matter.

"It got to the point where he thought he had to drink to deal with the situation," the court was told.

"He went home and sat in his room and began drinking. He drank himself into oblivion that night."

Mr English said Lock suffered nightmares that night and felt unwell when he woke, but he kept drinking.

"He then made a decision to make some sort of grand statement which then involved committing the offence," he said.

"He was not only very intoxicated, he was very agitated as well and also in a very emotional state.

"It was not his intention to harm anyone but it's plain the way he conducted himself was very dangerous. All he can do is apologise profusely for his conduct."

Prosecutor Carmen Matteo said the threats had been petrifying and highly dangerous for those at the office.

"The threat was an ongoing and an escalating one," she said.

"It exposed innocent victims to a frightening situation in a circumstance where they were entitled to feel safe in their workplace.

"This is a man who has a history of using or threatening to use fire for a punitive or remonstrative purpose."

Lock will be sentenced in a fortnight.