In essence, devolution is a way of enabling Scotland, Wales and Northern Ireland to have forms of self-government within the United Kingdom. The UK Parliament has conferred various sorts of legislative powers on the elected Scottish Parliament, National Assembly for Wales and Northern Ireland Assembly to do this.
The devolved legislatures in Scotland and Wales are quite small. The Scottish Parliament has 129 members and the National Assembly for Wales 60. Both are elected by the additional member system (very similar to the mixed member plurality system used in Germany and New Zealand). Some MSPs or AMs are elected on the first past the post basis, from single-member constituencies. This accounts for 73 MSPs and 40 AMs. The remainder are elected from regional lists, on a second ballot, and are allocated to try to ensure that there is proportional balance between the parties in those regions, taking into account the party affiliation of constituency MSPs or AMs.
The Northern Ireland Assembly has 108 members at present (the UK Parliamentary Voting System and Constituencies Act 2011 will reduce it to 96 after the next Assembly elections). They are elected using the single transferable vote system in multi-member constituencies.
Legislative devolution is accompanied by executive devolution to the Scottish Government (formerly Executive), Welsh Assembly Government and Northern Ireland Executive. Those governments are each accountable to their respective Parliament or Assembly.
All three devolved parts of the UK are still represented in the UK Parliament at Westminster as well. Scotland has 59 Westminster MPs, Wales 40 and Northern Ireland 18.
What devolution isn’t
Because it combines self-rule with shared rule (through Westminster), devolution has something in common with federal arrangements in countries like Australia, Germany or Canada. However, there are also many differences. The most important of these is that the UK Parliament remains sovereign in law and can still legislate, in theory and in fact, for Scotland, Wales and Northern Ireland. By convention (the so-called Sewel convention), it does not do so for devolved matters without the consent of the devolved legislature concerned.
A second major difference between the UK and federal systems is that England is outside the devolution arrangements. Scotland, Wales and Northern Ireland now each have two governments and legislatures, but for England there is only one – the UK Parliament and UK Government. This in turn gives rise to many of the asymmetric features that are characteristic of devolution, and which create many of its constitutional anomalies.
A third major difference between the UK and federal systems is that the nature of devolved powers varies between Scotland, Wales and Northern Ireland. Scotland’s legislative powers include policing and criminal justice; Northern Ireland’s don’t, as yet, but they do (formally) include social security. Both Scotland and Northern Ireland have devolved powers to legislate for any matter save those expressly excepted or reserved to Westminster. Wales, by contrast, has much more limited legislative powers in only those areas where powers have been expressly conferred on the National Assembly. This is another set of asymmetries about devolution.