I think I'm probably repeating what's above to some extent, but having just gone through the process of faith school applications with a DS, you do need to do the hard work of looking at the admissions criteria for each individual faith school as they do vary.
To illustrate using boys' schools, Cardinal Vaughan literally don't look at distance, only at faith criteria - I don't know if any girls' schools may do likewise, but you'll only know from reading their website. Others, e.g. Wimbledon College, it's a combination of faith and distance e.g. those with a baptism certificate and priest's reference who live in catchment come first. Specific out of catchment deaneries may get a couple of places allocated for those fulfilling faith criteria - who will leapfrog unbaptised in-catchment children. It's always on the school website, but if you are currently in a faith primary, your head should be able to give you information, and you may even find your parish priest can also help, if he's asked to do priest's references every single year, as ours is.