Coalition MPs Dean Smith, Trent Zimmerman, Tim Wilson, Trevor Evans and Warren Entsch. Credit:Alex Ellinghausen If that doesn't happen, Liberals who want change could take matters into their own hands. 2. Liberal MP introduces private members' bill Liberal senator Dean Smith last month confirmed he was in the "advanced" stages of drafting a bill to legalise same-sex marriage, including significant exemptions for religious organisations that don't wish to participate in same-sex unions. It could be introduced as private members' business in the Senate - or in the House of Representatives by another supportive Liberal MP, such as Trent Zimmerman.

Any same-sex marriage bill would not pass the government-controlled lower house without a number of Coalition MPs crossing the floor. Credit:Andrew Meares 3. Bill passes the Senate This is likely but not guaranteed. The government does not control the Senate and it is very likely Senator Smith's bill would be debated, and probably passed, with the help of Labor, the Greens, Nick Xenophon's trio, Derryn Hinch and David Leyonhjelm. The numbers would be close, but a same-sex marriage bill should be able to pass the Senate. Credit:Alex Ellinghausen But the numbers are close, especially because a handful of socially conservative Labor senators tied to the Shoppies union cannot be relied upon to support the bill.

4. Bill goes to selection committee Things are trickier in the House, where the government-controlled selection committee, chaired by Speaker Tony Smith, decides which bills come up for debate. If Prime Minister Malcolm Turnbull holds firm, the committee won't allow a same-sex marriage bill to be debated, but there is another way: to interrupt the usual business of the chamber. 5. Liberals cross the floor Suspending the standing orders requires an absolute majority of 76 out of 150 votes. Labor starts with 68 (Kate Ellis is on maternity leave), plus the presumed support of Adam Bandt, Andrew Wilkie, Rebekah Sharkie and Cathy McGowan.

To get to 76, four Liberals would need to cross the floor. Likely contenders are thought to be Mr Zimmerman, Trevor Evans, Tim Wilson and Warren Entsch, but it's possible more would be willing. 6. Bill passes the lower house Once it comes to a vote, marriage equality should easily pass the lower house. In 2015, former prime minister Tony Abbott said the previous term of Parliament was the last one in which Liberals would be bound to vote against same-sex marriage. In other words, they now have a conscience vote. Liberal MP Jason Wood this week said he would vote "Yes", in line with his conscience if standing orders were suspended - and expected many colleagues to do the same. But there are also a number of obstacles:

1. The plebiscite If the government decides to retry the plebiscite, or move to a voluntary postal vote that doesn't require legislation, Liberals would expect their colleagues to support this course of action. 2. Threats Reports have emerged of Liberal MPs including Mr Wilson and Mr Evans being threatened with preselection challenges in their seats if they cross the floor. 3. Tactics

If renegade MPs decide to proceed with their not-so-secret plan, the sequence isn't clear. They could decide it is tactically more effective to start in the House of Representatives rather than the Senate. 4. Timing Loading There is a tentative deadline of mid-September, when Mr Entsch leaves for a three-month secondment at the United Nations in New York. Labor senator Gavin Marshall will also attend that secondment. Follow us on Facebook