I have a bit of an application problem.
I've contacted several head of labs asking about PhDs for admission in October next year (I'm doing a masters in the meantime). Most of them have replied back saying look for advertised posts later in the year. It seems to be general protocol to talk to the head of the lab to which you are applying before you make the application, so does this reply count? Can I just apply straight away when the studentship is advertised on the basis that I've already made contact with the lab, or is some further, more detailed communication required right before application?

Well it would probably be worthwhile contacting them again once you see a studentship you like.. They are highly unlikely to remember your enquiry from this year..