Malcolm Turnbull will mark his first anniversary as Prime Minister by introducing the bill for a same-sex marriage plebiscite.

But the only way that legislation can pass is with Labor's backing and Bill Shorten is increasingly strident in his opposition to it.

The Opposition leader told Parliament that in the lead up to the leadership change a year ago Mr Turnbull said he believed a free vote in Parliament was the best way to go.

"Why are we led by a man who will, when knowing the best option, recommend to Australians a second best option? That is moral cowardice," Mr Shorten said.

For Tony Abbott, it is a year today since he lost the prime ministership.

"I really don't want to go over the entrails of the events a year ago," Mr Abbott told Sky News.

"Of course they were disappointing. Of course I think it should not have happened.

"But it did happen, and as many people say and rightly so, we have got to look at the world as it is rather than the world as we would like it to be or as maybe even it should be."

Mr Shorten is using the anniversary to critique Mr Turnbull's performance.

"This Prime Minister is the great national disappointment. From Messiah to mediocrity; from agile to fragile," he said.

Malcolm Turnbull makes his leadership pitch on September 14, 2015. ( AAP )

Morrison to continue Senate crossbench appeal

But Treasurer Scott Morrison is pleased the Government has notched up a win by forcing Labor to agree to vote for $6 billion of savings.

He is critical of the Opposition for not being prepared to go further.

"They are largely tapped out on the issue of things they are prepared to do on savings — one thing they are very enthusiastic about doing is actually lifting taxes," Mr Morrison said.

He told Sky News he will keep trying to negotiate with the Senate crossbench to try and pass some of the measures Labor remains opposed to, like removing the energy supplement from pensioners.

"We got rid of the carbon tax so going forward we are not going to give you the compensation for a tax that doesn't exist," Mr Morrison said.

"Now we are not walking away from that measure just because the Labor Party chose not to support that … we do support it and we want to see that passed and so we will now obviously go and deal with the crossbenchers in the Senate."

But that will be challenging after the double dissolution election Mr Turnbull decided on earlier this year.

The Senate has more crossbenchers and new members like One Nation's Malcolm Roberts, who gave his first speech yesterday calling for Australia to leave the United Nations.