Egypt's official religious advisor have declared that Muslims are free to change their religion - a statement that could significantly impact the status of Muslims who convert to Christianity and the county's Christian population in general.

"The essential question before us is 'can a person who is Muslim choose a religion other than Islam?' The answer is yes, they can," the Grand Mufti Ali Gomaa said in a posting on a Washington Post-Newsweek forum and picked up by the Egyptian press on Tuesday, according to Agence France-Presse.

The Grand Mufti is the highest official of religious law in a Sunni Muslim country. His opinions and interpretations of Islamic law assist the government in regulating civil laws but are not binding.

"The act of abandoning one's religion is a sin punishable by God on the Day of Judgement," explained Gomaa, emphasising that faith is a matter between an individual and God. "If the case in question is one of merely rejecting faith, then there is no worldly punishment."

However, Gomaa noted that if the conversion challenged the "foundation of society" then it should go through the judicial system, though he did not elaborate.

Egypt has an estimated 10 million Coptic Christians - the Orthodox Christians of Egypt and the largest group of Christians in the Middle East.

Despite the fact that Christians makes up 10 per cent of Egypt's population, the minority group has long been oppressed by the country's Muslim majority. They are isolated from mainstream society and are often forced to convert to Islam through rape, marriage, change of legal name and violence, according to Cameel Halim, chairman of the Coptic Assembly of America.

Egypt's Coptic oppression has for too long been "hidden under the table" and "no one knows what is going on", lamented Halim at a recent gathering of persecuted religious minorities in Washington DC.

Yet Muslim-background Christians face even greater obstacles than believers from Christian families.

Muslims who want to legally change their religion status to Christian on official documents are refused by the state and in some cases are arrested and imprisoned.

"Even though it is not a criminal offence in Egypt, they get detained under emergency laws or are put on trial for contempt of religion if they wish to convert," said Hossam Bahgat of the Egyptian Initiative for Personal Rights, according to AFP.

Also, converts to Christianity are still legally Muslims, they cannot legally marry Christians and their children are considered Muslims.

In the Islamic world, some extremists have even called for the killing of apostates.

"This (ruling) is significant, especially coming from Gomaa," said Bahgat. "Between 2004 and now there have been many court cases involving Christian converts to Islam that want to convert back to Christianity who are unable to do so."

Bahgat is involved in the upcoming case of the 12 former Christians who want to revert back to Christianity.

Earlier this month, Egypt's Supreme Court agreed to hear the appeal of the Coptic Christians. The case was denied by a lower court in April, which had ruled against the converts. The lower court had argued that recognising such a case would be considered apostasy under Islamic law.

The case of the 12 Copts will go to the Supreme Court in September. Bahgat said they will use Gomaa's posting to support their case.

"Gomaa is a civil servant, the top religious advisor of the state, and technically speaking the deputy minister of justice," Bahgat said. "So his views on the matter carry authority."