Labor’s unconvincing performance on Senate voting reform reached new levels with the extraordinary speech by frontbencher Gary Gray in parliament on Wednesday.

Labor this week has been going through contortions as it opposes the government’s proposed changes.

The short version of its travails is this. The ALP originally agreed Senate voting reform was necessary, and was part of drafting bipartisan recommendations made by the parliamentary committee on electoral matters.

What’s being proposed in the legislation the government introduced this week is based on these recommendations, although not precisely the same. But Labor then split, as the factional hardheads feared the changes would most likely benefit the Coalition. As expected, the opponents of change prevailed in shadow cabinet on Monday.

Labor MPs have struggled to prosecute the new line, arguing the reforms would in effect exclude those who did not vote for the main parties (including the Greens) and making other objections. But their credibility has been undermined by the switch the party has made.

There are points to be contested about aspects of this bill but Labor’s overt expediency means it comes to the debate tarnished, with a weak case. Now Gray’s speech has dealt the opposition’s position a major blow, attacking its arguments while publicly admitting he had been rolled in his party.

From time to time backbenchers from both sides tip a bucket on their party’s position.

But Gray is not speaking as a backbencher. He could have been. Last week he announced that he would not recontest his Western Australian seat of Brand and had offered his resignation from the frontbench.

Bill Shorten hasn’t accepted that resignation. Gray remains as shadow special minister of state – which includes electoral reform.

In his speech Gray said that “fixing the Senate voting system is as important as one vote, one value. It is an important as the franchise itself.”

“A fundamental principle of voting systems is that a voter should actually intend to vote for the candidate or party with whom their vote finally rests. Because of the ability to manipulate the current system, the present Senate voting process now fails this test.”

Gray rejected the contention, made by Labor, that the changes were intended to stifle or prevent the formation of new parties. “These reforms simply mean that political parties, including my own, will have to convince the public rather than backroom dealmakers that they deserve their votes.”

He also dismissed suggestions the new system would increase the informal vote, or deliver the Coalition a controlling majority in the Senate, tabling modelling by the Parliamentary Library to refute the latter point. And he was scathing about the claim from Labor and others that the changes would cut out the more than three million people who voted for other than the main parties.

“We are told that their votes will be wasted or voided … Votes count.”

He was astonished that “the kind of dumb view that, if you vote for someone who loses … your vote is wasted” had taken some hold during the discussion.

Gray said that he “lost the argument in my party room on Senate reform, so Labor will oppose the substantive reforms that are enshrined in this bill. I think that is sad, but it is a reality. My party has moved that it will be opposing this bill and therefore I oppose this bill.”

In the circumstances, Shorten certainly should accept Gray’s resignation. That would mean an awkward reshuffle – Gray is also resources spokesman – and Shorten might not want to rock that boat. But the idea that one retains a spokesman who not only doesn’t agree with the party’s policy in his area but surgically dissects it in parliament not only defies all convention but is surely a nonsense.