Foreign Minister Alexander Downer torpedoed a deal to slash convicted drug smuggler Schapelle Corby's 20-year jail term in half with "irresponsible" comments about her case, Corby's legal team says.

The Bali High Court this week shortened Corby's sentence to 15 years following a protracted legal appeal and several trial reopenings in the lower Denpasar District Court.

Lead lawyer Hotman Paris Hutapea said he would fight on like a "kung-fu teacher", even though he was doing the case for free and it had already cost him as much as a new Ferrari.

The High Court decision was "inhumane" because no other prisoner in Indonesian courts had ever received more than five years for possessing less than 10kg of marijuana, he said.

The Gold Coast woman was jailed after customs officers at Denpasar airport found 4.1kg of marijuana in her unlocked bodyboard bag last October.

Hutapea said he would begin lodging an appeal to the peak Supreme Court in Jakarta on Monday and the plea would be filed within a fortnight.

He said judges in the Bali appeal court had been ready to deliver a 10-year cut by knocking back Corby's trafficking sentence to a lower charge of drug possession.

But he accused Downer of ruining the deal when the foreign minister spoke in Sydney on August 19 of rumours Corby's sentence would be halved.

Downer also said there was no way of confirming the rumours.

Hutapea, speaking at a press conference in Jakarta attended by Corby's sister Mercedes and Indonesian film celebrity Sophia Latjuba, said: "Canberra ruined this case by issuing a very bad public statement.

"Unfortunately ... your foreign minister, the foreign minister of Australia, make a very irresponsible public statement to the public, and very speculative to the public, by saying that the High Court already issued a decision by cutting 10 years."

Because of Downer's comments, local reporters had rushed to see the court chief Made Lingga, angering the judges.

"This attitude really ruined our strategy, because it looked like somebody from us leaked out the information," the flamboyant millionaire counsel said.

"We don't understand what is the motive of Alexander Downer."

Hutapea and co-lawyer Erwin Siregar said a letter to the Supreme Court requesting a teleconference to hear new evidence from Australia on who really owned the marijuana found in Corby's luggage would create a new legal precedent or "breakthrough".

Normally the court only considers evidence already presented to the lower courts.

Siregar said the Bali prosecutor would also lodge a counter-appeal challenging the sentence reduction.

Mercedes Corby said Downer's comments and the diplomatic wrangling over her sister's case had turned Corby into a political prisoner, rather than a drug convict.

"Australian Federal Police in Australia never searched her car, her house, anything," she said.

"They are just letting her take it. Maybe she is more of a political prisoner now than another prisoner.

"Our government should be doing something to help."

Australian Schapelle Corby will appeal against her drug conviction to Indonesia’s Supreme Court, one of her lawyers said today.

"We will keep fighting," Hotman Paris said, days after a high court upheld her guilty verdict, but decided to reduce her 20-year prison sentence by five years.

Corby, 28, was devastated by Tuesday’s ruling. She claims she is innocent, and had hoped her conviction would be overturned.

The 28-year-old beauty student was sentenced in May for smuggling 4.2 kilograms of marijuana onto the Indonesian resort island of Bali.

Paris said the defence team was filing an appeal with the Supreme Court, which would be asked to review existing evidence.

Dozens of foreigners are imprisoned for drug smuggling every year in Indonesia, but Corby’s case sparked public outrage in Australia, where many people believe she did nothing wrong.