He stressed the need to show compassion to women who have suffered as a result of going through with an abortion.
"To those who have had an abortion, God is here to meet you with His love and forgiveness" as well as "hope, healing and a new start", he said.
The service included readings and prayers from a number of notable Christian figures, including Pastor Ade Omooba, CARE's Nola Leech, Jim Dobbin of the All Party Parliamentary Pro Life Group and Joel Edwards, General Director of the Evangelical Alliance.
In October 1967, the Abortion Act received royal assent and abortion was legalised in Britain. Since then 6.7 million abortions have taken place, and a harrowing 465 more are taking place every single day.
Andrea Minichiello Williams, public policy officer of the Lawyers' Christian Fellowship said: "This is a important moment in the life of the church in this country and it is a moment for us to come together as the corporate body of Christ to repent for where we have not stood up on behalf of God's truth with regards to the sanctity of life and marriage, and with hearts of compassion for the women caught in unwanted pregnancy.
"Never has there been a more important time for Christians to stand in the public square to witness truth and compassion at the heart of our culture. This could be the key to unlocking revival and true repentance."
The Christian Medical Fellowship's Head of Communications Dr Andrew Fergusson said: "The Abortion Act was passed two years before I went to medical school. At first I was unaware of it but when I became a GP ten years later I faced the reality of abortion requests on at least a monthly basis.
"Since then, the numbers have continued to rise, reaching the highest ever, and after forty years, with 6.7 million abortions, one English woman in three having an abortion, and almost one in four pregnancies ending in abortion, I think indeed it is time for change."
He added: "All Christians everywhere must become aware of the enormity of this problem and pray and work towards reducing the numbers of abortions."
