Legal Action against hospital/trust

Anyone got any experience or advice re legal action to force change of treatment or more specifically, to get a referral to a more suitable institution? Mumsnet posters suggest exhausting internal procedures first, which is reasonable and has started...wonder if anyone knows a legal firm that specialises? The problem is that once you are officially under the care of a hospital team, only they can refer you elsewhere, and if they choose not to.....?