The law about this is a bit complicated, but basically there is no law protecting people from being treated badly because of their religion. The complicated bit is that, in practice, some people are protected:

• Jews are classified as a 'racial group' under the Race Relations Act because they have what's called a 'common heritage'. This means that almost all Jews are the children of Jews (it is possible to convert, but it is rare) and that people born as Jews tend to still call themselves Jews, even if they are not at all religious. Jews have also experienced such persecution that it would have been impossible not to have included them in the law. The persecution, especially under the Nazis, was not because of their religious beliefs.
   
• Sikhs are also classified as a 'racial group' under the Race Relations Act because they have common roots: a language and culture as well as religion in the Punjab area of north west India. They are not physically any different from Muslims and Hindus from the same area.
   
• In Northern Ireland everyone is protected against discrimination at work on the grounds of their religion. Because of the history of conflict between two branches of Christianity - Protestants and Catholics - the Fair Employment Act was passed. This protects people whatever their religion, so Muslims are covered too.
   
• Christians are protected against their religion being publicly insulted by the blasphemy laws. These were passed many years ago when almost the whole population would have said they were Christian, and when the Christian religion was much more a part of everyday life. No-one has been punished for this crime for a long time, but it seems odd that it's a crime to insult the god that Christians believe in but not a crime to insult the god that Sikhs believe in.
   
• If some rule unfairly discriminates against a particular religion, then it may be that its followers are protected by the Race Relations Act if they all belong to one ethnic group. This is called indirect discrimination. (Example: strictly speaking it would be legal for a shop in Leicester to advertise for staff saying 'only Christians need apply', but since there are many Asian Hindus in Leicester, and not many Christians, they could say that indirectly the advert discriminates against them.
   

Muslims are the largest religious group in Britain not protected by the law. They cannot be classed as a racial or ethnic group because Muslims do not have a long, shared history; they do not have a particular place they all come from, and they do not share a common language or a common culture. Many feel quite strongly that the law ought to protect them as Muslims, not solely as people who happen to have dark skin. Mosques have been attacked, people get threats over the phone, abuse gets shouted at children, not because they are Asian but because they are Muslims.