I agree with the general point that the non-religious should get a say in how the country is run proportional to their proportion of the population.
I'm not sure Dawkins' argument about state funded faith schools is very strong. If the church is dying (which it is) and the religious schools have a disproportionate amount of pupils, then the religious schools are not indoctrinating their pupils very well. Even though they often select children from families that claim to be religious, those children do not emerge as a new wave of missionaries.
The better claim is that they divide society. Anecdotally, I went to a CofE aided primary that gave a certain amount of priority to the children of church attenders, but still admitted around a dozen Sikhs and Muslims every year (in a year group of 70) and some people who were explicitly non-religious or from other Christian backgrounds. I tried to look into literature on this and there appears to be very little. The best I could find was this evidence provided by Dr Rebecca Allen and Professor Anne West: http://www.publications.parliament.uk/p ... c31102.htm
I have no reason not to believe Dr Allen, so I will presume she is telling the truth about her findings. She says that religious schools effectively select for social class, and uses free school meals as a barometer, which I think is a good measure. This effect is only marked in London and the north west, but of course it's still a concern, even if it is a concern largely limited to two regions of the country.