The Blair administration came to power in 1997 promising referendums on devolved administrations in Scotland, Wales and London.
In all three cases the electorate voted in favour of devolution and by 2000 the respective administrations had been established.
Meanwhile, the 1998 Good Friday Agreement for peace in Northern Ireland, backed by the majority of the population in both Northern Ireland and the Irish Republic, led to the creation of a new Northern Ireland Assembly.
All four new administrations have their own parliaments and electoral systems as described below, some using the same constituencies as the UK (Westminster) Parliament, others using their own.
Please note however that ONS Geography does not maintain constituency listings specific to the devolved parliaments.
The Scottish Parliament, founded in 1999 and sitting in Edinburgh, has a total of 129 MSPs (Members of the Scottish Parliament).
73 MSPs are elected directly from single member constituencies and the remaining 56 are elected via a proportional system using eight electoral regions that coincide with the eight pre-1999 European Parliament seats.
The Scottish Parliament appoints a First Minister, who in turn appoints other ministers to form the devolved government known as the Scottish Government.
The Government is in turn accountable to the Parliament.
National Assembly for Wales
This was also founded in 1999 and sits in Cardiff with a total of 60 AMs (Assembly Members).
40 AMs are elected directly from single member constituencies and the remaining 20 are elected via a proportional system using five electoral regions that coincide with the five pre-1999 European Parliament seats (same idea as the Scottish system, see above).
The National Assembly for Wales appoints a Presiding Officer, who in turn appoints other Assembly ministers to form the Assembly Cabinet. The Cabinet is the main decision-making body of the Assembly and is accountable to it.
The Cabinet is the main decision-making body of the Assembly and is accountable to it.
Changes were made to the boundaries of the Assembly constituencies and electoral regions in May 2007.
Northern Ireland Assembly
From 1921 to 1972 Northern Ireland had its own Parliament but, as a result of the Troubles, direct rule from Westminster was implemented in 1972.
The 1998 Good Friday Agreement re-established the principle of home rule and a new 108-member assembly was elected via a proportional system in each of the existing 18 Westminster constituencies.
After an initial delay caused by disputes over the appointment of ministers, the Assembly first sat in 1999 in Stormont Castle, Belfast.
Assembly members are known as MLAs (Members of the Legislative Assembly).
The government of Northern Ireland is known as the Northern Ireland Executive.
The Assembly appoints the First Minister and Deputy First Minister.
Each political party in Northern Ireland is allocated a number of government departments, reflecting the size of that party's representation in the Assembly, and the respective Executive ministers are selected by that party.
The Executive is accountable to the whole Assembly.
Prior to its abolition in 1986, the administrative area of Greater London was controlled by the Greater London Council (GLC).
Thereafter the 32 boroughs and the City of London Corporation became single-tier administrations.
In 1998 though a referendum revealed a large majority in favour of re-creating a single authority to deal with London-wide issues, and the new Greater London Authority (GLA) was established in 2000.
The elected components of the GLA are the Mayor of London and the London Assembly.
The Mayor is elected directly, and London Assembly elections occur at the same time.
The Assembly has 25 members, 14 of whom are elected directly from constituencies formed from groupings of either two or three London boroughs, and 11 of whom are elected using a city-wide proportional system.
The Assembly works together with the Mayor, and also has the role of regulating and scrutinising the Mayor's decisions.