FORMER Liberal prime minister Malcolm Fraser will campaign with the Greens to prevent Tony Abbott gaining control of the Senate, should he win the upcoming federal election.

Fairfax reports that Mr Fraser will campaign with Greens senator Sarah Hanson-Young, who is competing against the Liberal Party for the sixth and last Senate spot in South Australia.

Mr Fraser controlled the Senate for the first five years of his three-term prime ministership, from 1975 to 1980, but he is now estranged from the Liberal Party, which he left in 2009, saying it had become too conservative.

The Greens have been calling on voters to keep them in the Senate to prevent opposition leader Tony Abbott from controlling both houses of parliament, although the return of Kevin Rudd as prime minister indicates a mammoth coalition victory is less likely.

Senator Hanson-Young and Mr Fraser will co-host a sold-out public question and answer forum at an inner-city Adelaide cinema on Saturday afternoon.

Mr Fraser is very critical of both major parties' policies on asylum seekers, as is Senator Hanson-Young, the Greens spokeswoman on the issue.

South Australian Liberal frontbencher Jamie Briggs dismissed suggestions Mr Fraser's actions - and his views on asylum seekers - were damaging for the coalition.

"It's not surprising," Mr Briggs told Sky News. "Malcolm Fraser has made his views known on these issues for a very long time.

"Malcolm Fraser's entitled as a citizen to his views. We don't agree with them."

Originally published as Malcolm Fraser to campaign with Greens