The Government is to be challenged over its failure to fund legal representation for a British woman sentenced to death for drug smuggling in Indonesia, a law firm has said.

Grandmother Lindsay Sandiford, 56, from Cheltenham, Gloucestershire, was given the death penalty by a court in Bali last week for taking 10.6lb (4.8kg) of cocaine onto the island.

The sentence, which will see her shot by a firing squad on the beach, was even more harsh than the 15 years in jail requested by the prosecution. She has seven days to launch an appeal, but has no legal representation.

Law firm Leigh Day, which is working with the charity Reprieve, said it would cost around £2,500 to pay for an adequate lawyer to take on her case, but the British Government will not pay.

The firm said Sandiford had not been properly represented since her arrest at Bali airport in May last year, when customs officers found the drugs sewn into the lining of her suitcase. A lawyer who specialised in property and had no experience of capital cases represented Sandiford at her trial, Leigh Day stated in a letter to Foreign Secretary William Hague.

Rosa Curling, from the firm's human rights team, said: "The UK Government has repeatedly confirmed its opposition to the death penalty. It has a clear legal duty to ensure our client, who has no money to be able to pay for the basic essentials, let alone legal representation, receives appropriate assistance to be able to file an appeal against her death sentence.

"Without the Government's help, Ms Sandiford faces being executed by firing squad. Mr Hague must not allow this to happen - he must immediately ensure Ms Sandiford, a British citizen, is provided with the opportunity to challenge her sentence and file an appeal."

The firm is seeking a judicial review of the Government's decision not to pay the £2,500 legal expenses for Sandiford, who is originally from Redcar, Teesside. A hearing at the High Court in London will be held before Thursday.

The Foreign and Commonwealth Office said the Government does not fund legal representation for British nationals abroad, but Sandiford's case was being raised through diplomatic channels. A spokesman said: "We strongly object to the death penalty and continue to provide consular assistance to Lindsay and her family during this difficult time.

"We have made repeated representations to the Indonesia authorities and the Foreign Secretary raised Lindsay Sandiford's case with Dr RM Marty Natalegawa, Indonesian Foreign Minister, during the recent November State Visit of the Indonesian President."