In 2013, the coalition Government set out a new strategy for local growth. This encouraged local authorities to collaborate more and to put regional economic development at the heart of their governance. The main legal mechanism for this is a new kind of public body: the combined authority, made up of two or more local authorities, sharing powers covering their combined areas.

The core purpose of a combined authority is for local authorities to deliver enhanced local economic growth by working together more ambitiously. A combined authority is also a way to meet requirements set by national government to devolve resources to a local level through devolution deals.

The founding primary legislation for combined authorities is the Local Democracy, Economic Development and Construction Act 2009 (the 2009 Act). Under the 2009 Act, a combined authority is created by secondary legislation in the form of a Parliamentary Order, made by the Secretary of State for Communities and Local Government. A combined authority's Parliamentary Order triggers powers available under the 2009 Act, allowing a combined authority to take responsibility for local government functions in its area, for example transport, economic development and regeneration.

A combined authority's Parliamentary Order can therefore confer a range of responsibilities on it. These include any local government function, or any public authority function. A combined authority's Parliamentary Order can also provide for an elected combined authority mayor. Accordingly there are two broad types of combined authority: those with a mayor for its area, and those without a mayor. The legislation does not allow for a combined authority in London.

Wider primary legislation beyond the 2009 Act specifies certain powers available to a combined authority. For example, under the Bus Services Act 2017, a combined authority may make a bus services franchise scheme as the franchising authority for its area. A combined authority Parliamentary Order may then exclude a constituent council from being the franchising authority for its individual council area, so that the combined authority itself is the exclusive franchising authority for all the local council areas that make up its combined authority area.

As a legal entity, a combined authority exists wholly within the public sector, unlike a company owned by a joint authority or local authority.

As of July 2017, there are nine combined authorities. In our notes on them, we summarise their key functions and powers conferred by their Parliamentary Orders.