BBC Writer's Room provides basic advice on script writing, a library of radio and TV scripts that can be downloaded for free, upcoming opportunities for submitting scripts (the BBC has a window/room open for submitting different types for defined periods only). There is also a blog with information on shows and if I recall correctly they provide some basic analysis on scripts received from time to time. If you sign up you can leave comments. There are also interviews etc etc etc - loads really - take a look
My experience of submitting (once) and looking at an analysis of a previous window was that 88% of submissions get kicked out after a 10 page read. I can't remember the rest - I think a few more get a 20 page read, some get a full read and very few get passed to the team (something like that).