The Mongolian woman who entered Singapore illegally by boat last year, to try to snatch her toddler son from his grandparents, has won in her battle to get the custody hearing held in a London court.

The 30-year-old is in the process of divorcing her Singaporean husband of four years, who had wanted the wardship case to be heard here.

The three-year-old boy, whom she failed to snatch, is currently living in Singapore with his paternal grandparents.

None of the parties can be named for legal reasons.

In judgment grounds released last month, Justice Jennifer Roberts ruled that the hearing should be held in the High Court in London.

She turned down the father's bid to move the case to Singapore, pointing out that both parents are in London and the woman would be disadvantaged were the case to be held in Singapore as it is unclear if she would be allowed to enter the country.

Justice Roberts said: "There needs to be a swift resolution to these proceedings... in order for matters to move on for this child."

She added that events to date had "taken their toll emotionally and financially on each of (the boy)'s parents" which "was plain to see as they sat in court".

The couple married in Singapore in 2011 but lived in London where the man worked as a bank analyst. Their son was born in July 2012 but the marriage began to falter and they took him to Singapore to live with his grandparents before returning to England without him in 2013.

The father subsequently filed for divorce in Singapore while she did the same in England. After a British judge ruled the son's habitual home is London, she obtained a court order for his return there.

The judge noted that the mother is in a "distraught" state, having not seen her son for more than a year.

The grandparents have refused to let her have any contact with him and the judge noted that the grandfather accused her of being an "extremely selfish person" who is "only interested in how she can benefit financially through the marriage".

The 36-year-old father has regular Skype and telephone contact with his son and is barred from leaving London, where he will face criminal charges of rape and violence against the mother in October.

The grandparents have so far refused to take part in the London custody proceedings.

Last October, the boy's mother made headlines here when she was jailed 10 weeks and deported to London after she and a former British policeman illegally sailed into Raffles Marina from Langkawi and tried to snatch her son from his grandparents.

Justice Roberts found the boy's father and grandparents had the financial means to hire specialist lawyers here but the mother had none. She noted the mother's snatch plot last August might also be seen as "desperate actions of self-help".

Justice Roberts held that the woman would be disadvantaged if the case was heard in Singapore, as she lacks the finances of her husband and his parents.