Tasmania's Premier has labelled maverick Liberal Speaker Sue Hickey's decision to vote against a government bill on mandatory sentencing as disappointing but says his majority is not under threat.

Key points: Tasmanian Speaker Sue Hickey voted against the Government on mandatory sentencing for serious child sexual assaults

Tasmanian Speaker Sue Hickey voted against the Government on mandatory sentencing for serious child sexual assaults Speaker cited serious concerns among the legal profession about the changes

Speaker cited serious concerns among the legal profession about the changes Premier Will Hodgman vowed to pursue them and said his majority was not under threat

The Government's plans to introduce mandatory sentencing for serious child sexual assaults are dead in the water after the Speaker used her casting vote to block the bill.

The Hodgman Government had made it an election promise to re-introduce the legislation after it was voted down by the Legislative Council in 2017, and has claimed a mandate for the policy after taking it to two separate elections.

Last month Ms Hickey consistently voted against the Government to pass landmark legislation to make gender optional on birth certificates.

Hodgman insists he still has majority

Premier Will Hodgman said he was disappointed in Ms Hickey's decision to vote against the sentencing bill, but insisted the Liberals' majority was not in question.

"I'm disappointed because I think our policy position is sound," he said.

"We've known for some time that we won't always get our way in Parliament. Some legislation will get through and other not, but it's our job to keep moving ahead with our agenda.

"We have a majority and we intend to deliver on it. We won't be distracted by the parties, most notably the Labor Party, who will try to disrupt what we do in Parliament."

Mr Hodgman added the Government stood by the policy and would continue to pursue the laws.

Despite being elected on the Liberal ticket last year, Ms Hickey said serious concerns about the legislation raised by legal professionals had convinced her not to support its passage through the Lower House.

Ms Hickey split with colleagues to leave one of her party's key policies dead in the water. ( ABC News )

"A lot of the key policies are just headline statements and a few words," she said today.

"So you know, being tough on crime sounds great and it is great in concept.

"But when it actually comes down to the detail in a piece of legislation, then you have to analyse it word-by-word."

Last night, Ms Hickey said she was surprised to see a bill which was previously defeated by the Legislative Council brought back to Parliament without any changes.

"There are significant concerns from the legal profession who do not support this removal of authority from the judges to do their jobs," Ms Hickey told the House.

"It is the judges who understand the complexity of the case before them.

"In this regard I take the view that the professionals who know a lot more about the law, and who believe this is bad law which does not give effect to desired outcomes or better ends — in fact it may have unintended consequences to the detriment of the victims.

"Parliament should never make laws based on popular opinion … it should only ever be made on informed advice."

Ms Hickey said it would have been easier for her to support the legislation, which she conceded was a "popular choice", but she said "it is braver and truer to my own conscience to not support this bill in its current form".

The State Opposition had earlier attempted to move the legislation to a parliamentary committee for investigation, after floating a policy to increase the maximum penalty for child sexual assaults to a life sentence, rather than introduce mandatory minimum sentences.

The Greens voted against the move, and Ms Hickey said she was disappointed the legislation would not be considered in committee.

'They're trying to push through legislation that won't work'

Labor Shadow Attorney-General Ella Haddad congratulated Ms Hickey for voting against "badly drafted" and "not well consulted" legislation.

"They're trying to push through legislation that won't work, and people are seeing through that type of gutter politics these days. It's no coincidence that this is happening just a few days before three Legislative Council elections," Ms Haddad said.

"The Government has brought out this law and order debate over and over again, election after election. The Parliament is seeing through this, the Speaker Sue Hickey has seen through it, and the people of Tasmania can see through it as well."

Following the vote, the House of Assembly moved on to debating similar mandatory sentencing laws for assaults against off-duty police officers.

Ms Hickey voted with the Government to support that legislation, saying although she was conflicted over the bill, a number of police officers had "begged" her to support it.

Tasmanian Attorney-General Elise Archer had said she believed Ms Hickey would support the bill. ( ABC News )



On Monday, Attorney-General Elise Archer said she was confident the Government would have Ms Hickey's support to pass the legislation.

"I believe we would — I believe the Speaker is fully supportive of this move," she said.

Ms Hickey today said she always listened to the full debate before making a decision on how to vote.

"I hadn't had any conversations with the Attorney-General, so that was disappointing," she said.

Ms Hickey snatched the Speakership in controversial circumstances a year ago, declaring she would vote independently on government bills.