Hours before Foreign Office representatives were due to meet with staff at the Pakistan High Commission in London, the Prime Minister insisted the UK Government was doing everything in its power to express its opposition to the death sentence handed to Mohammed Asghar.
In answer to a question by Edinburgh East MP Sheila Gilmore during Prime Minister's Questions, he said: "I too am deeply concerned about this death sentence passed onto Mr Mohammed Asghar and, as you know, it's our long-standing policy to oppose the death penalty in all circumstances.
"But in these authorities, the Pakistani authorities can be of no doubt of the seriousness with which we view these developments."
Speaking from the despatch box, he added: "(Foreign Office Minister) Baroness Warsi spoke to the Chief Minister of the Punjab on Monday, our High Commissioner in Islamabad continues to raise this case with the relevant authorities, Foreign Office officials are meeting Pakistan High Commission officials in London today to discuss his and other cases.
"We take this extremely seriously and we're making that clear at every level."
Labour MP Ms Gilmore had asked: "Mohammed Asghar, who has lived in the UK for 40 years and has family in my constituency, has recently been committed of blasphemy and sentenced to death in Pakistan.
"Mr Asghar was diagnosed with paranoid schizophrenia in 2010 and was treated in Edinburgh, but the judges refused to take that into account.
"I wrote to the Foreign Secretary yesterday, but can you now assure me that you and your ministers are doing everything they can to support this man and to see him returned to the UK where he can get the treatment he needs?"
Mr Cameron replied: "I can certainly can give you the assurance that you have asked for."
Mr Asghar, a 69-year-old grandfather, received the death penalty after writing letters to people claiming he was the Prophet Mohammed.
The capital punishment order against the elderly Briton, who returned to Pakistan in 2010, was made late last week and questions have been asked about the nature of the trial after lawyers were blocked from visiting him on numerous occasions.