The driver behind one of Australia’s worst bus tragedies has failed in his attempt to have his jail sentence reduced, after a court rejected his appeal over the mass-fatality crash.

Brett Andrew Button, 60, was given a decades-long term for causing the 2023 Hunter Valley disaster that killed 10 wedding guests – most of them young – and injured another 25.

He had been driving at excessive speed and under the influence of the opioid painkiller Tramadol when his bus overturned at a roundabout in Greta.

The sentencing judge said that in more than 50 years working within the judicial system, he had never encountered a case that caused such widespread devastation.

Seven of the victims were from Singleton, many connected to the local AFL club, including coach Nadene McBride, her daughter Kyah and Kyah’s partner. Others were from Queensland or from the married couple’s hometown of Melbourne.

Button appealed his 32-year sentence, arguing that several of the 35 charges he pleaded guilty to had been improperly double-counted.

On Friday, the NSW Court of Criminal Appeal dismissed the challenge, leaving intact both the full sentence and the 24-year non-parole period.

His barrister, Paul Rosser KC, contended the punishment was excessive.

“As catastrophic as the consequences were of the applicant’s dangerous driving, the aggregate sentence imposed was manifestly unjust and unfair,” he wrote in submissions.

Button also argued the sentencing judge was wrong to find he knew he was affected by Tramadol, and wrong to accept that the bus could tip at just 31km/h. He maintained he had taken the drug for years without feeling impaired.

However, Director of Public Prosecutions Sally Dowling SC told the court Button should have been aware of its effects, noting he had previously been dismissed from employment when his employer discovered his addiction.

The bus had been carrying wedding guests from a winery when it entered an elliptical roundabout en route to Singleton and overturned, striking a guardrail.

“This next part’s going to be fun,” Button told passengers before accelerating into the roundabout and taking the turn at speed moments before the vehicle tipped.

Survivors later described believing they were about to die.

“The sensation of falling sideways and being completely powerless was terrifying,” Jason Junkeer told Button’s sentencing hearing.

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