Much of the information that has to be sent to Companies House must be registered on one or more of the official forms. There are at least 105 of these at the last count. The Companies Act 2006 considerably increased the number of forms required to be registered by companies, and most forms are more complex than their 1985 Act predecessors. For example, the form to be completed on first registration of a company used to be three pages long. Its successor is much longer and more complex, as you can see.
Even then, not all information can be sent on an official form. Many resolutions must be sent to Companies House as signed copies of the resolution passed, and either there is no official form, or the copy of the resolution must be sent with the official form.