When to make the first filing can be a difficult decision. The sooner the first application is made the less likely it is that a competitor will file for a similar invention. This is a particular risk with companies working in a particular area of technology, who may come up with the same invention, or overlapping inventions, frequently within a few months of each other. The company which files first usually scoops the pool.
However, the invention must be sufficiently well developed to allow working examples to be filed within one year of the application. They would ideally be included at the time of the application itself so there is a balance to be struck.
An additional factor in favour of an early filing in the UK and other European Patent Convention (EPC) countries is that if your patent application is filed and not yet published it forms part of the state of the art for the purposes of assessing novelty against a later application (section 2(3), Patents Act). It is not however relevant for the purposes of the ‘inventive step’ requirement.
In the UK, an application for a patent must contain a request for grant of a patent on the appropriate form, give contact details for the applicant, and be accompanied by the requisite fee (currently £30). In addition your application must contain a description of the invention (the specification) or alternatively a reference to an earlier application for the same invention. (Section 14(1) and (2), Patents Act.) Without these, the application cannot be given a filing date.