This is also a bit of what I got from the Department of Energy & Climate Change.
Consumers will have control over who has access to their data, apart from where this is required for billing and other regulated duties. As part of the data access and privacy framework, suppliers will be allowed to access monthly data for billing purposes. Customers may opt out from allowing suppliers to access daily data, or opt in to allow suppliers to access half-hourly data. Suppliers will be required to explain clearly to their customers which data is being used, for which purposes, and what choices the consumer has about this. Thus, if a consumer has opted in to giving the supplier access to half hourly data, then the supplier will be allowed to collect information covering half hourly periods.
Energy UK has published a Data Guide which explains which data will be accessed from the smart meter, for which purposes, and what choices customers