The Supreme Court has said Lindsay Sandiford, the grandmother on death row in Bali, "remains in jeopardy" and is in "urgent need of legal help".
The 57-year-old from Cheltenham has lost a battle at the UK's highest court over the lawfulness of a Government policy not to provide funding for legal representation to Britons facing capital charges abroad.
Five Supreme Court justices in London unanimously dismissed a challenge by Sandiford, who was convicted last year of trafficking drugs into Bali and sentenced to death by firing squad.
The Supreme Court called on the Government to carry out an urgent review of whether funding for legal representation can be given in the case.
Grandmother Lindsay Sandiford, who is on death row in Indonesia for trafficking drugs to Bali, has lost her latest battle at the UK's highest court to get funding to fight her case.
Sandiford, 57, from Cheltenham, Gloucester, was sentenced to death by firing squad after being arrested in May 2012 for smuggling 4.8kg (10.6lb) of cocaine worth £1.6 million from Bangkok.
She claimed she was forced to transport the drugs to protect her children, whose safety was at stake.
An appeal against her sentence was rejected but she is continuing to fight her case.
However, she is currently without legal representation and tried to challenge the lawfulness of a Government policy not to provide funding for Britons facing capital charges abroad.
But today five judges in the Supreme Court unanimously dismissed her case ruling the policy was lawful even in death penalty cases.
A human rights charity has called for the Government to "step in" and help a British grandmother who lost her appeal against a death sentence for trafficking drugs into Bali.
This will be devastating for Lindsay and her family, following months of torment throughout the appeals process.
Without a lawyer to seek the new evidence needed for the Courts to re-review her sentence and prepare her clemency petition, Lindsay faces extremely difficult decisions.
We hope that the British government will step in to ensure that Lindsay is at least provided with a lawyer to help her avoid execution.
The Foreign Office said it would "consider how to support any application for judicial review or clemency" that Lindsay Sandiford makes after she lost her appeal against a death sentence for drug trafficking.
A Foreign and Commonwealth Office spokesman said: "We are aware that Lindsay Sandiford's appeal to the Indonesian Supreme Court has been denied.
"We will continue to provide consular assistance to Lindsay Sandiford and her family at this difficult time."
A British grandmother has lost her appeal against a death sentence for drugs trafficking in Bali, a spokesman for the Supreme Court in Jakata confirmed.
A three-judge panel at the court unanimously rejected Lindsay Sandiford's appeal, Ridwan Mansur said.
The judges agreed with the decision taken by Bali's Denpasar district court, which sentenced Sandiford to death, and the island's high court, which rejected her first appeal.
Under Indonesian law, Sandiford still has the opportunity to seek a judicial review of her case before appealing for a presidential pardon.
Lindsay Sandiford was sentenced to death after being found guilty of drug trafficking in January.
Sandiford's alleged accomplice, Julian Ponder, from Brighton, was jailed for six years in Bali after being cleared of drugs smuggling but convicted of possessing drugs. He remains in jail.
His partner, Rachel Dougall, also from Brighton, received a one-year jail term and has now returned to the UK after serving her sentence.
Paul Beales, a long-time Bali resident, was sentenced to four years in prison for possession of hashish. He remains in jail.
The Foreign Office is seeking confirmation that a British grandmother has lost her appeal against a death sentence for trafficking drugs into the resort island of Bali.
We are aware of unconfirmed reports that the decision of the Indonesian Supreme Court has been announced. We are seeking confirmation of the decision from the Indonesian Supreme Court.
We will continue to provide consular assistance to Lindsay Sandiford and her family at this difficult time.
A woman from Teesside appears to have lost her second, and possibly final, appeal against a death sentence in Indonesia.
Lindsay Sandiford faces a firing squad after being convicted of drug smuggling in January.
The 57-year-old from Redcar had been arrested at Bali Airport after drugs were found in her luggage.
The Foreign Office has told ITV News that they are checking reports that her final appeal has been rejected,
If this is the case, her last hope would be a presidential reprieve.
Human rights campaigners expect Indonesia's Supreme Court to make a decision in Lindsay Sandiford's case "within 96 days" from her lodging an appeal today.
Zoe Bedford, from legal charity Reprieve, said:
Lindsay remains extremely grateful to the generosity of the public in raising the funds to allow her to file this appeal.
We are hopeful that the Supreme Court will take into consideration the compelling mitigating evidence in Lindsay's case and award her a sentence that is proportionate both to the offence and to her role in it.
In particular, it is hoped that the judges will give due consideration to Lindsay's cooperation with the authorities which led to the arrest and prosecution of more senior syndicate members, and take into account the need to encourage others to cooperate in the future.