OCR does not specify which religion you study, and the exam questions are open - they refer to 'the religion you have studied' or 'religious ethics'. However, most text books discuss Christian Ethics. This is partly because Christianity is, in terms of number of adherents, by far the largest religion in the UK, and is to my knowledge the only religion that must be studied at school (locally agreed syllabuses vary, but all must include Christianity). In discussing medical ethics, Christianity has had a greater influence on the law in the UK than any other faith. The most influential politicians (Blair and Brown at the time of writing) are Christians. Also three of the ethical theories studied (Natural Law, Situation Ethics and Virtue Ethics) originated with or were developed by Christians.
For students of other faiths or no faith, studying Christian ethics gives a better understanding of the current legal position in the UK. For Christian students, it gives the opportunity to challenge traditional views (for example about homosexuality) in an informed and thoughtful way.
Natural Law [more]
The Roman Catholic Church accounts for the majority of Christians in the world, and is the largest religious organisation of any religion. Within Catholic theology, Natural Law holds a dominant position. The Church encourages a range of different approaches, but when it comes to offical church teaching, the vast majority of statements, encyclicals etc. are strongly in-line with Natural Law.
Within other denominations, Natural Law theology still has a significant impact. Many Christians adopt deontological positions and think we should act according to God's design or purpose for our lives. They may be less influenced by Aquinas in this, and Protestants tend to be less sure about moral absolutes. However, there is still a strong sense of following rules within most Christian denominations.
Situation Ethics [more]
It is difficult to guage the influence of Situation Ethics. Even before Fletcher wrote his book, many theologists supported a 'love ethic':
"There is only one ultimate and invariable duty, and its formula is "Thou shalt love thy neighbour as thyself". William Temple, 1917
"The law of love is the ultimate law because it is the negation of law." Paul Tillich, 1951
There is a tension within the Christian faith between the command to love, and the sense of duty towards other commandments and obligations. Fletcher saw the need for rules, but he said we need to be ready to abandon them when love demands this.
The challenge of situation ethics is so great that some Catholic theologians believe there needs to be a compromise between Natural Law and Situation Ethics. 'Proportionalism' (the title of a book by Brtitish philosopher Bernard Hoose) accepts, as Natural Law does, that certain acts are wrong or evil acts in themselves. However, it says that it might be the right thing to do, if there is a proportionate reason, to perform such acts.
The arguments here get quite tricky, and proportionalism ends up looking a lot like situation ethics. Proportionalists claim that doing a 'bad' action out of love makes an action morally good but not morally right. A 'bad' action is only morally right if it is proportionate. This is familiar from Just War thinking.
Virtue Ethics [more]
Virtue ethics sits very comfortably next to Natural Law - Aristotle was a proponent of both theories, as was Aquinas. Within the Christian traditions there has been great support for the 'cardinal virtues', listed on this site as wisdom, judgment, temperance, and courage. It is common to see them called prudence, justice, temperance and fortitude, although they refer to the same virtues.
Christianity added to the virtues. There are the theological virtues: faith, hope and love. There are also the 7 capital virtues (although the accompanying 7 deadly sins are better known):
Within Protestant churches, a much greater emphasis is put on the Bible. Without a God-given authority to put faith in, Christians are expected to read the Bible for themselves and make their own decisions about important ethical issues. However, without the ability to read scripture in the language in which it was written, Christians have to put faith in the translators. On issues such as homosexuality, the translators' bias comes through in the translation, with words such as 'abomination' used with no justification.
Reading the Bible raises other issues. Is it the literal word of God, or merely inspired by God? Is it possible to dismiss large chunks as having been written for people in an entirely different society?
The best way to read the Bible is to look at the context of any passage. What is that passage meant to mean to the person who was going to read it? While parts of the Bible have a clear meaning, and are inspiring to many Christians, there will always be debate about the true meaning of some difficult passages.
Within Protestant churches, the church has an advisory role. It can recommend one action over another, it can condemn certain actions entirely - you can even be kicked out of the church for certain actions. However, the individual is still left to decide where to stand in relation to church teaching. In Protestant churches, the Bible has a much greater authority than the church.
This is a large number of important factors to lump together. Christians can get inspiration from the indwelling of the Holy Spirit. Many Christians believe the conscience to be 'the voice of God'. The vast majority of Christians pray for guidance even when they wouldn't pray for intervention (some Christians don't ask God to actually solve their problems, but those who pray tend to believe that God responds or gives answers to prayer). Some Christians have had a direct, life-changing experience of God, which may mean seeing a vision, hearing a voice or feeling God's presence.
All of these factors can have a profound effect on the individual and can contribute significantly to the ethical decision-making process. However, because they are personal and individualised, there is very little to say other than to recognise their importance, and that this can lead to a wide variety of different Christian responses.