Money

I've never yet earned money from screenwriting. That's what my day job is for.

Surprisingly, there are standard rates of pay for screenwriters, courtesy of the Writers' Guild of Great Britain. I didn't even know there was a Writers' Guild of Great Britain.

It seems I can expect to receive at least £2700 for writing the treatment, at least £9450 for a first draft script, and at least £3240 for a second (or fourteenth) draft.

(For interest, compare the Writers Guild of America rates - almost double on average.)