Reserved and excepted matters

In the United Kingdom reserved matters and excepted matters are the areas of government policy where the UK Parliament had kept the power (jurisdiction) to make laws (legislate) in Scotland, Northern Ireland and Wales.

Each of these countries has been granted devolution within the UK; therefore some power has been delegated to them from the central government at Westminster and some has been withheld.

They are also known as reserved matters and act as a guide for which areas are devolved to those three countries and which are not. The powers are set out in three main laws for each of those countries and subsequent amendments which further devolved powers to the respective legislatures:

In Scotland, a list of matters is explicitly reserved in the Scotland Act. Any matter not explicitly listed in the Act is implicitly devolved to the Scottish Parliament. Reserved powers can be transferred from Westminster to Scotland under Section 30 of the Scotland Act 1998, for example in the Edinburgh Agreement, 2012.

In Northern Ireland, the powers of the Northern Ireland Assembly do not cover reserved matters or excepted matters. In theory, reserved matters could be devolved at a later date, but excepted matters were not supposed to be considered for further devolution. In practice, the difference is minor as Parliament is responsible for all the powers on both lists and must give its consent to devolve them.

In Wales, by contrast, a list of matters is explicitly devolved to the National Assembly for Wales and any matter not listed in the Act is implicitly reserved to Westminster. Wales will move to a reserved powers model once the provisions contained within the Wales Act 2017 are put into effect.

...
Wikipedia