I thought this was a legal requirement from the solicitors?
I keep an eye out on sold prices and have noticed that some houses that exchange hands never show up. (Either as a sale at all. or a sale with the sold price.)
They are often the more expensive houses too! I found something online where someone said that if property is sold as part of a company it won't show up. Interestingly some of the homes I've looked at have been bought / sold by people who own a company (sometimes working from home as a consultant) so might they be registering it as a company address and therefore avoiding the sale price appearing?