With around 21,000 registered voters, it has the smallest electorate of any constituency in the United Kingdom. It is expressly protected from being combined with other constituencies by the 2011 Parliamentary Voting System and Constituencies Act.
The constituency area is that of the Outer Hebrides, known also as Na h-Eileanan Siar, and the constituency has the smallest electorate in the United Kingdom, one-fifth of the size of what was, until the 2024 United Kingdom general election, the largest, the Isle of Wight, which is also an island constituency.[needs update] However, the Isle of Wight is a substantially smaller parliamentary constituency in geographical terms. It has been suggested that Na h-Eileanan an Iar could be combined with the Orkney and Shetland constituency: the resulting combined electorate would still be well below the average constituency quota. The seat's entire turnout at elections will be less than a winning candidate's vote in a rural English seat.
The Scottish Boundary Commission in 1980 proposed that the seat should be extended to include the Skye and Lochalsh areas; this was overturned at a public enquiry. Generally, considerations of geographical size, a disparate population and convenience for the MPs concerned, as well as tradition and identity, have tended to override the arguments about numerical imbalance. Furthermore, a change in the Boundary Commission's rules in 2000 added a rule which forbade Orkney or Shetland being combined with another council area. In 2011, the Parliamentary Voting System and Constituencies Act 2011 was introduced, which prevented both Na h-Eileanan an Iar and Orkney and Shetland from being combined with any other constituency.[2]
The seat had been a two-way marginal between the Labour Party and the Scottish National Party for many years. In 2005 it became a safe seat for the Scottish National Party. This trend was reversed in the 2017 general election, when the SNP suffered a swing against them for the first time since 1997, but at the 2019 general election the constituency became a safe seat for the SNP again, but at the 2024 general election the seat heavily swung to Labour. For the Conservatives, their vote has increased in recent years, since losing their deposit in the 2005 and 2010 elections, but once again lost their deposit at the 2024 election.
During the 2014 Scottish independence referendum the constituency voted against independence by a margin of 53.42% (10,544) to 46.58% (9,195) in favour on a turnout of 86.2%[3]
The constituency is notable for having the highest percentage of Scottish Gaelic speakers of any constituency in the world.[citation needed]