Legally it has been laid down by parliament that parents are entitled to express a preference as to the school that they want their child to attend. This is why parents always get those forms from the council asking them if they want to specify a school, and about the time when a child is about to move up from one school to another. Councils do not do this out of the goodness of their heart, they do it because they are legally required to do it.
However, the same legislation then goes on and spoils it a bit by giving to the council the right to override that preference and do whatever they want if they wish to do so. So the supposed right of parental choice is rather empty in many cases.
If the council chooses to exercise this right and allocate a different school then the parents have a right of appeal to a School Appeals Committee, which is suppose to be independent of the council. In fact what tends to happen in practice is that the School Appeal Committee of one council will be independent in the sense that it is made up very largely of people from the neighbouring Council and vice versa.
There are literally thousands of school appeals every year, and if you find yourself in this position you should consult a good lawyer about getting some representation.