British and Saudi authorities have declined to comment on the woman's case but it is understood that she told an Asylum Tribunal that she would face the death penalty under Sharia law, reported Telegraph.
The woman, who has been granted refugee status and anonymity, is married to an elderly member of the Royal Family of Saudi Arabia and met her non-Muslim English boyfriend during a visit to London.
She became pregnant the following year and persuaded her husband to let her return to the UK so she could give birth in secret.
She has now become one of a handful of Saudi citizens to apply to the UK courts for asylum. Such cases are not generally acknowledged by the British government for fear that highlighting the persecution of women in the strict Muslim nation would strain relations with the House of Saud.
The woman told the Immigration and Asylum Tribunal that she could be liable to death by stoning under Sharia law if she returned, or face an honour killing.
Since she fled her home country, her husband's family and her own, independently wealthy family, have broken off contact with her.
A spokeswoman for the Home Office in London refused to confirm the report, saying it did not comment on individual cases. A spokesman for the Royal Embassy of Saudi Arabia in London was unavailable.
According to Amnesty International, there were at least 102 executions of men and women by stonings, floggings, beheadings and hangings last year and the charity claims there are at least 136 more people on death row.
Last week, the kingdom's religious police were blamed for the shooting dead of two sisters by their brother in Riyadh in what was deemed to be an "honour killing".
The sisters, who were 19 and 21, had been arrested by the police for allegedly mixing with men to whom they were not related, a move which according to The Society for Defending Women's Rights, prompted the killing.