pawncob wrote:You can register as self employed at any time, but your business doesn't start until you actually make a sale.
I disagree. Your trade starts when you have a product that is ready to sell and try to sell it; there is no need actually to sell it.
http://www.hmrc.gov.uk/MANUALS/bimmanual/bim70510.htm
So I suggest it commences on the date that you start touting your book/idea/whatever around agents/publishers. The date on which you first feel you have something that would be saleable and try to sell it.
The £100 penalty is fixed. You can't avoid it. Why would you want to register in 2008? There are no benefits.
He states the benefit is in his wife's immigration. Personally, as there is no tax riding on when you do commence, I don't see any problem in registering back dated to 2008. They can only refuse to accept your registration which will save you £100, and they're not going to. Whether it makes a difference with the immigration authorities I do not know.