MARK COLVIN: The Prime Minister has raised the possibility of a referendum at the next election, to strip the Senate of some of its power to block legislation. He says his idea is similar to one floated by former Labor Attorney-General Michael Lavarch. Both propose a joint sitting of Parliament to vote on legislation blocked repeatedly by the Senate.

But there are differences, as Rafael Epstein reports.

RAFAEL EPSTEIN: The Prime Minister has a raft of bills that have been blocked by the Senate. Under the current rules, he could call a double dissolution election where every seat in the Senate and the House of Representatives is up for grabs.

After that, there's a joint sitting, where every Senator and member of the House of Representatives sits in the same chamber and votes on the previously blocked bills. Now, he's proposing a referendum to change that system. As he told Channel 9, one idea he'll air is from former Labor Attorney-General Michael Lavarch.

JOHN HOWARD: Mr Lavarch's proposal was that you provide an option for the Prime Minister to call a joint sitting, rather, immediately after an ordinary election, that is an election for the House of Representatives and half the Senate if legislation has been twice blocked in the previous Parliament.

Now, the subtle but important difference between that and the raw proposal I raised provides a mix of the current procedure, which involves an election to be interposed between the rejection and the passage at a joint-sitting. The only difference is that it's an ordinary election.

RAFAEL EPSTEIN: But that is not what Michael Lavarch is proposing. Mr Lavarch wants a joint sitting after the re-election of the whole Senate – very similar to the current double dissolution election that John Howard currently wants to get rid of.

The difference is important because Senate seats are won under proportional voting. A party gets a number of seats based on the percentage or proportion of votes it receives in each state. Under a full senate election, because 12 senators and not 6 would be elected from each state that halves the amount of votes needed to gain each seat.

The ABC's electoral analyst Antony Green.

ANTONY GREEN: It means that you'll probably get two minor party candidates from every state.

RAFAEL EPSTEIN: What likelihood is there then, that a Government could go to an election, have an election for all of the Senate and all of the House of Representatives, yet come back and when there's a joint sitting – when all the senators and members of the House of Representatives sit together – they might not have a majority, they might not have the numbers? Is that a possibility?

ANTONY GREEN: That's a possibility. I mean, it's a possibility if we have a double dissolution next year that John Howard would strike that possibility – he doesn't get a big enough majority in the House to get the numbers at a joint sitting.

RAFAEL EPSTEIN: So, Michael Lavarch's proposal is very different to John Howard's because all of the Senate is voted out or has to be voted on each time and that could dramatically alter the composition of a joint sitting?

ANTONY GREEN: I'm not too convinced whether that is the case. I think, in fact in moving to electing the whole Senate at once may result in there also being some need to change the electoral system in the Senate.

Under the current system, with full preferential voting and ticket voting, you can get the situation that occurred in the New South Wales Upper House several years ago, where a candidate with a very low vote got elected because of preference deals.

You can probably guarantee in every state there'll be one candidate elected who no one's every heard of, because of the way preferences work. That's because we're electing too many, with 12 senators, in using this system.

If the Michael Lavarch path of electing the whole Senate at a time is taken, I think it's also probable that they'll have to change the electoral system in some way.

RAFAEL EPSTEIN: The Labor Party is unlikely to back Mr Howard's idea, a fact that the Prime Minister says will stop him moving forward with it. In 1988, a referendum pushing for a very similar proposal to Michael Lavarch's was opposed by the Liberal Party. They said it would give too much power to the Prime Minister and weaken the Senate.

MARK COLVIN: Rafael Epstein.