South Australia failed on Wednesday to decriminalise prostitution due to the lack of one vote. The state Parliament's lower house vote 20-19 in favour of retaining the present law on sex trade.

The result of the voting could have been changed were it not for the absence of eight MPs, two of whom were locked out because of late arrival.

The private member's bill by Labor MP Steph Key proposed to decriminialise all types of prostitution such as those done at home and in brothels, escort services and those who walk the street. However, the bill excluded soliciting of clients when done in the presence of other people.

Among the eight absent MPs were SA Premier Jay Weatherill and Treasurer Jack Snelling who were at the Techport facility in Osborne for the visit of U.S. State Secretary Hillary Clinton. One MP was confined in the hospital.

Ms Key said some of the absent MPs were expected to support her bill, so she is seeking advice if she would recommit the legislation at a later date when these MPs would be present. Because of this circumstance, the result of the Wednesday vote is not an indicator of support for the measure, she added.

However, Family First MP Dennis Hood was happy with the bill's defense because it would legalise the sex trade minus state government control.

Besides the call for another vote, there are also suggestions to amend the parliamentary system in the state to allow MPs more notice of conscience votes.

There is a similar private member's bill in SA Parliament's Upper House authored by Labor Status of Women Minister Gail Gago. The legislation is expected to be debated in about two weeks.

Prostitution has been decriminalised in some Australian states such as New South Wales about 15 years ago. Groups that campaign for decriminalisation of the sex trade in other Australian states cite that it would keep workers in the industry safer.

A research made in the early 2000s found that 15.6 per cent of male Australians aged 16 to 59 paid for sex at least once in their live and 1.9 per cent in the past 12 months.