Britain will mark the 40th anniversary of the day the Abortion Act came into force on April 28, 1968.
Studies by the Guttmacher Institute and the World Health Organisation, published last October, show the number of abortions worldwide fell to less than 42 million in 2003 from 46 million in 1995.
Here is an overview of the abortion law in some countries:
UNITED KINGDOM - Abortion has been legal in Britain since 1968 for pregnancies up to 24 weeks. The British law does not apply to Northern Ireland, which retains many restrictions on abortion.
CHINA - The world's most populous country with 1.2 billion people, China limits most families to one child and encourages abortion as a way of controlling population growth.
INDIA - With a population of more than 1 billion, India allows abortion within the first 12 weeks of pregnancy if a qualified doctor says it is necessary to save the mother's life.
-- If the pregnancy is more than 12 weeks but less than 20, two registered medical practitioners must agree an abortion is necessary. The written consent of the woman, or of the guardian if the woman is under 18 or mentally challenged, is required for an abortion.
AUSTRALIA - Abortion is not legal in six states and two territories, but is officially allowed if a woman's life is at risk. Many women circumvent the law using 1960s and 1970s common law rulings which permit abortion on social and economic grounds. Restrictions on abortion vary by jurisdiction and women are allowed abortion on demand in the state of Western Australia.
EUROPE - The legal abortion period is 10 weeks in France, Greece, Denmark, Norway and Portugal, 12 weeks in Germany, Belgium and Austria and 22 to 24 weeks in Britain, Spain, Switzerland and the Netherlands. Malta, Ireland and Poland still have highly restrictive abortion laws.
ITALY - Abortion was legalised in Italy in 1978 and upheld in a referendum in 1981. The law allows abortion on demand in the first 12 weeks of pregnancy and until the 24th week if the mother's life is at risk or the foetus is seriously malformed.
RUSSIA - Russia was the first country to legalise abortion in 1920, although the law was repealed in 1936 and abortion remained illegal until 1955. Abortion requires the consent of the pregnant woman and should be performed by a licensed physician in a hospital. It is allowed on request during the first 12 weeks of pregnancy, and between 12 and 28 weeks from conception on judicial, genetic, vital, broad medical and social grounds, and for personal reasons with the special authorisation of a commission of local physicians.
POLAND - The 1993 law allows abortion only if pregnancy threatens a woman's life or health, results from rape or incest, or if the foetus is irreparably damaged. In 1996 it was liberalised to allow women to end a pregnancy before the 12th week because of poverty or other social problems.
MUSLIM COUNTRIES - Islam bans the abortion of a living foetus, but some countries like Syria allow abortion in cases where there is a pressing medical need, such as a danger to the mother's health.
ISRAEL - A woman may terminate a pregnancy if she is not married, or if the pregnancy is the outcome of rape or poses health risks. Abortions are also allowed for women younger than 17 or older than 40.
SOUTH KOREA - The law allows abortion only if the mother's health is at risk, the baby has severe defects or if the pregnancy is caused by a sexual crime. Doctors can face up to two years in prison or lose their licence for illegal abortions, though very few cases have come to court.
PHILIPPINES - Women who terminate a pregnancy risk prosecution and up to six years in jail. Abortion is legal if it is necessary to save a woman's life. Every year nearly half a million women have abortions in the Philippines despite legal restrictions.
UNITED STATES - The Supreme Court in its landmark Roe v. Wade decision in 1973 ruled by a 7-2 vote that women have a constitutional right to an abortion, making abortions legal throughout the nation. In 1992, the court allowed some new restrictions as long as they do not impose an "undue burden" on pregnant women.
CANADA - Abortion has been legal, for any reason at any time up to delivery, since the Supreme Court struck down an anti-abortion law in 1988.
Sources: Reuters; United Nations - www.un.org/esa/population/publications/abortion/index.htm; World Health Organisation
(Writing by Nagesh Narayana, editing by Kate Kelland and Tim Pearce)