Should twins be put in separate classes at age 4? Should the parents have the final decision?

My twin 4 year old girls will be starting Reception class this September. I have been informed that it is school policy to separate twins into different classes. My daughters are not entirely dependant on each other, they in fact have completely different personalities and have different interests. If they were very co dependant i could see that it would benefit them. But they are not. i have always done my best to treat them equally, and allow them to develop their own personalities, and they have done that very well. They have been together since before day 1, and have no problems so far, Has anyone else been through a similar experience? is there any law to say this has to happen? This is a school policy not a government or council policy. My Daughters are very upset at the thought of being in different classes, and i am struggling to decide what to do. I have been told basically i have until today to make a decision and if i don't agree to them being separated, i will have to remove them from the school. School places are limited in my area and I do not see why my children should have their schooling disrupted. Any help or knowledge anyone can offer is very much appreciated.