I live in the UK and earn part of my income through freelance creative work. So far, this freelance work has been short, one-off contracts. So I just file a tax return on my year's earnings and pay the tax as required.
This year is different, because I have been commissioned to write a book. I have a received a modest advance on my work and I stand to earn more if the book sells well. Of course beyond the advance I have no way of knowing how much my book is going to earn me.
A friend told me that there are special tax rules that allow authors to split the income from something like a book over multiple years. The logic goes that full-time authors (which I am not) may make a large sum in a year where they publish a book, but may not publish again for several years. So by spreading their "income", they can pay tax at a more consistent and sensible rate.
I have been unable to find any mention of this in the HMRC help online. Is it correct? If so, how does it work?