A land owner with an outline permission has to get their reserved matters approved before carrying out the development. A reserved matters submission is not in legal terms a planning application. It does not have to be made on an application form (but usually are) and ownership certificates are not needed. There is no requirement for neighbours to be consulted on the application, but in practice most authorities do so. The application should be in accordance with what has been approved at outline stage, e.g. if a certain floor area for the building is specified, though a slight deviation might be considered acceptable. Not all the reserved matters have to be submitted in one application and the application does not necessarily have to cover all the development, e.g. if the outline approval is for several buildings, only the details for one could be submitted. It is possible for more than one set of details to be approved – the developer would then have to decide which one to build.
More information can be found on the Planning Portal.