Ann Furedi at the British Pregnancy Advisory Service (BPAS) - a leading abortion provider - said abortions can be necessary when regular contraception "lets them down".
Christian pro-life group 40 Days to Life told Premier preventing a pregnancy is very different from ending one.
Board member and family physician, Haywood Robinson said: "Contraception basically is the process of preventing a pregnancy - abortion is the ending of pregnancy which results in the death of a child so they aren't the same thing."
The abortion organisation, which carries out 60,000 abortions each year, called for an end to restrictions on terminating pregnancies after carrying out research which revealed half of all women questioned in their clinics were using contraception when they became pregnant.
Robinson said this didn't suffice challenging the law governing the termination of pregnancies for the past 50 years.
He added: "Pregnancy is a side-effect of intercourse - it's going to happen and contraception - regardless of what method - is not 100 per cent so a person who is using contraception should expect the possibility that they may get pregnant."
The 1967 abortion act says abortion is a crime unless approved by two doctors and in cases where there is a risk to the health of the woman or her children.
Listen to Haywood Robinson speaking with Premier's Alex Williams:
