Labor's controversial bank tax proposal has passed South Australian Parliament's Lower House after securing the support of former Liberal MP Duncan McFetridge, but remains unlikely to succeed.

The Liberal Opposition had campaigned strongly against the $370 million levy, which the Government wanted to impose on the big banks.

The tax was announced as part of this year's state budget.

Today, the Liberals attempted to remove it from the Budget Measures Bill during a vote in the Lower House.

But that move failed to win the support of Mr McFetridge, who voted against his former colleagues' attempt to block it.

Mr McFetridge quit the Liberal Party earlier this year after failing to win pre-selection for his electorate.

The State Government had the numbers to pass the bill without Mr McFetridge's support, and the development does not alter the tax's long-term prospects.

The levy remains unlikely to get through the Upper House, where several crossbenchers have already indicated their opposition to it.