A study conducted by the Family Planning Association of Northern Ireland (FPANI) on women from both sides of the border concluded that more than 3,000 travel to Liverpool alone for abortions, twice the figure previously thought.
According to its findings, every year 2,000 from the Republic and around 1,000 from the North have terminations carried out in Liverpool.
The numbers are double those given by the British Pregnancy Advisory Service (BPAS), which recorded just over 500 women from the North as heading to the Merseyside clinics in 2002.
The reason for the divergence is that the NIFPA survey included Irish women who give English addresses and the BPAS conceded yesterday that their figures could be understating the true picture.
A spokesperson for BPAS in the North West of England said: "It is possible there are many more women coming over than our figures show. Obviously we would hope to be as accurate as possible but we can only report what our clients tell us, and we know some women will not want to give their real home address."
The director of the FPANI, Ms Audrey Simpson, said it was not uncommon for women to give false English addresses because of the stigma attached to abortion on both sides of the border.
"A local politician told me recently of a bus full of pregnant girls going to England," she said.
"Every single one of them had given false addresses."
The Northern Ireland figures also appear to undermine those quoted by the Irish Family Planning Association whose statistics are largely based on the British figures.
"Our figures show that more than 6,000 Irish women travel to all parts of Britain every year for an abortion," a spokesperson for the IFPA said.
According to their figures, between January 1980 and December 2001, at least 98,565 Irish women had abortions in Britain. But if the Northern Ireland figures also hold true for the Republic the real number could be much higher.