The issue was raised in a question posed by Lord Patten, and answered by Foreign Office minister Baroness Kinnock. By way of giving credit where it's due, here's the full exchange, reproduced from Hansard:
"Question: Asked by Lord Patten
To ask Her Majesty's Government what is their stance on the resolution promoted by the Organisation of the Islamic Conference before the United Nations General Assembly on the defamation of religion. [HL1038]
The Minister of State, Foreign and Commonwealth Office (Baroness Kinnock of Holyhead): The Government share the concern of the Organisation of Islamic Conference that individuals around the world are victimised because of their religion or belief. We all need to do more to eliminate religious intolerance and to ensure that those who incite hatred or violence against individuals because of their religious beliefs are dealt with by the law.
But the Government cannot agree with an approach that promotes the concept of "defamation of religions" as a response. This approach severely risks diminishing the right to freedom of expression. We believe that international human rights law already strikes the right balance between the individual's right to express themselves freely and the need for the state to limit this right in certain circumstances. International human rights law provides that only where advocacy of religious hatred constitutes incitement to discrimination, hostility or violence should it be prohibited by law.
We believe that the concept of "defamation of religions" puts in danger the very openness and tolerance that allows people of different faiths to co-exist and to practise their faith without fear. It risks changing the focus of international human rights law from examining how countries promote and protect the right to freedom of expression to censoring what individuals say. If this happened, people might feel unable to speak out against human rights abuses or hold their government to account. It is also inconsistent with the international human rights legal framework which exists to protect individuals and not concepts or specific belief systems.
For this reason the UK, along with our EU Partners and other like-minded countries, voted against the resolution put forward by the Organisation of Islamic Conference at the 64th session of the UN General Assembly on Combating Defamation of Religions."