The prime minister has been asked to help in the case of a British woman being held on death row in the US.
Linda Carty was born in the British dependent territory of St Kitts
Linda Carty, 45, was convicted of murder in February 2002, following the death of a neighbour who was kidnapped.
But the human rights charity Reprieve has said there is no forensic evidence and no eyewitness to link her to the crime that took place in Texas.
Her daughter, Jovelle Joubert has handed in a letter at 10 Downing Street.
Ms Joubert, who lives in Houston, has said that her mother's legal case needs the help of the British Government: "My mum's innocent and all we are asking for is the opportunity to prove it."
WOMEN ON DEATH ROW
10 Women executed in the US since 1984
9 Women executed in the last six years
47 Women awaiting execution
She added: "I would hope that Tony Blair would help her, to give us that chance to prove not only to him but the rest of the world she had nothing to do with it. If he would just help me save my mum's life."
Ms Carty is being held on death row at Mountain View prison in Gatesville, Texas but two appeals are currently lodged in the US courts.
Reprieve has said that she was denied the counsel of her choice and her court-appointed lawyer, who is handling 21 death row clients, more than any other lawyer in the US, has the worst record for execution cases.
The charity also says that as a drugs informer she was convicted on the evidence of three co-defendants, all of whom were involved in drugs and were given reduced prisons terms for their testimonies.
Ms Carty has British dependent territory citizenship because she was born on the island of St Kitts, in the Caribbean, to Anguillan parents.
She moved to America in 1981 but did not take US citizenship, although she has Legal Permanent Residence status.
Ms Carty's legal team says the UK Government was not notified of her British status at the time of her trial - when they could have offered assistance.