The UK has stepped in to support the appeal of a British grandmother sentenced to death for drug trafficking in Indonesia.

Britain’s Foreign and Commonwealth Office raised claims that Indonesian authorities mistreated Lindsay Sandiford by threatening the 56-year-old with a gun and depriving her of sleep in a document submitted to the Denpasar District Court in Bali as Sandiford appealed against her death sentence on Monday.

“The British government wants to attract the court’s attention to serious allegations of mistreatment by related officers and officials at the time Lindsay Sandiford was first detained,” the document read.

The document also cited the UN Convention Against Torture that outlaws forced sleep deprivation. Indonesia had ratified that convention.

Sandiford’s crime was “not exceptional enough” to warrant capital punishment, the document said, according to AFP.

This comes after the High Court in London dismissed Sandiford’s request for financial help in appointing a lawyer, estimated by the NGO Reprieve to cost 2,500 pounds ($1,134).

Rights groups have criticized Sandiford’s death sentence as “cruel”.

“She is clearly not a drug king pin – she has no money to pay for a lawyer, for the travel costs of defence witnesses or even for essentials like food and water,” Reprieve said.

Sandiford was sentenced to death by firing squad last month for smuggling nearly five kilos (11 lbs) of cocaine worth $2.4 million into Bali in May. Indonesian authorities believe Sandiford was operating within an international drug trafficking ring on the island.

“We strongly object to the death penalty and continue to provide consular assistance to Lindsay and her family during this difficult time,” Hugo Swire, junior minister at the Foreign Office, said.