The Boundary Commission starts work today on a review of parliamentary constituencies. The last successful review was implemented in time for the 2010 general election and was based on population data from 2000. This new review uses Office of National Statistics data from March 2020 (which registered a record-sized electorate of 47.6 million), to bring greater electoral responsiveness to demographic change. Any general election called after July 2023 will be fought using these new boundaries.

What are the likely differences that the review will make to constituencies and which parties stand to profit from the redrawing of boundaries?

Firstly, much has changed since 2011 when the Cameron-Clegg coalition announced – but never enacted – a reduction of the House of Commons from 650 to 600 MPs. There is nothing sacred about 650 as a number: in 1918 there were 707 MPs but by 1922 only 615 after southern Ireland ceased to be represented; but for most of the two centuries since 1800 the total has fluctuated quite narrowly between 630 and 670.  Reducing the size of the House to 600 would, therefore, have been a significant reform.

Self-interest more than honouring historical precedence motivated Westminster to derail so dramatic a reduction and Boundary Commission proposals in 2013 and 2018 were ditched. That saga has been concluded with the passage of the Parliamentary Constituencies Act 2020 last December, establishing in law that the size of the Commons will remain at 650.

The 2020 Act reaffirms the boundary integrity of three island constituencies: Orkney and Shetland, Na h-Eileanan an Iar (the Outer Hebrides) and the Isle of Wight (which will have two constituencies within it) and adds to this protected list Ynys Môn (Anglesey). For all other constituencies, the Boundary Commission is tasked with creating constituencies of more equal size.

As a result, the Boundary Commission has confirmed that England will gain ten new seats, taking its total to 543 constituencies. The Commission has announced it will review boundaries on the basis that the ‘quota’ size for each should be 73,393, with a variation permissible within 5 percent. So – apart from the protected island constituencies – no constituency will have fewer than 69,724 or more than 77,062 electors.

Achieving constituencies of this near uniform size cannot be a cookie-cutter operation or an attempt at psephology through blind algorithm. So long as it is within the 5 percent ‘quota’ range, the Commission still has latitude to also give due consideration to the relevance of existing boundaries, special geographical considerations, existing or prospective local government boundaries, the danger of breaking local ties and the inconveniences that change may bring. Wherever possible, it should it mindful of these factors.

When the Parliamentary Constituencies Act was passed last month, Chloe Smith, the constitution minister, said, “more equally sized constituencies is a sensible policy that will make our elections fairer, ensuring that people from all four nations of the UK have equal representation in Parliament.” For Wales and Scotland, this more equal representation will mean fewer MPs.

Scotland used to be significantly over-represented with 72 MPs, supposedly to compensate for being far away from Westminster and without its own legislature. In time for the 2005 general election this was cut to 59 to better reflect the UK-average size and in recognition of the revival of Scotland’s own parliament. The Boundary Commission for Scotland has confirmed that the new review will lop-off another two constituencies. Inevitably this is never welcomed where it appears to remove an advantage. The prospect of losing two Scottish seats “to the advantage of England” warned SNP MP David Linden in November, “strikes me as being wholly unfair.”

The big change is in Wales. The initially limited nature of devolution there allowed the principality to escape a cull. But the powers of what was originally the Welsh Assembly (now officially, Seneed Cymru) have increased and consequently Wales’s over-representation at Westminster will end. As a result, the Boundary Commission for Wales has announced a cut from 40 Welsh MPs to 32. By contrast, Northern Ireland will continue to have 18 MPs (to Sinn Fein’s delight an attempt by the Boundary Commission for Northern Ireland in 2018 to cut representation to 17 was struck down by the Court of Appeal).

Assuming that the courts do not determine otherwise on the mainland, what will these changes mean for the main parties? Lord Hayward, the Conservative peer and elections expert, calculates that on a 2019 voting pattern, the new boundaries would have added between 5 and 10 Conservative MPs. In the context of Johnson’s current majority, that is hardly a decisive shift. But it might have made a difference in the event of a hung parliament (in 2017 Theresa May ended up 8 seats short of a majority).

All gain/loss estimates are necessarily caveated, not least because the voting pattern at the next general election is unlikely to be a facsimile of 2019. The calculation would change if, for example, the Tories leak votes in the former “Red Wall” of northern constituencies they won and which, however drawn, revert to pre-Corbyn voting traditions at the next election. But there may be less pressure on the Conservatives from Remain-focused voters in southern constituencies. At this distance, no psephologist can make precise calculations about how boundary realignments may accentuate or diminish such shifts.

Voters throughout the United Kingdom will be more equally represented than at any time in the history of British democracy

However, the historic experience of Labour MPs being over-represented because of the smaller size of inner-city constituencies is less true than it was a decade or more ago. The new May 2020 data shows that Bristol West (held by William Wadegrave until 1997 but where by 2019 the Conservatives were trailing-in third behind Labour and the Greens), now has almost 100,000 electors, 13 percent larger than the number registered in December 2019. Other super-sized and still growing constituencies include Sheffield Central (safe Labour), Leeds Central (safe Labour) and Battersea (a more marginal Labour hold), each of which recorded electorate rises of between 10 and 12 percent over the same period. In such areas, boundary redistribution is likely to create more Labour MPs.

In Wales, where the revision will have the greatest impact, Lord Hayward points out that, “last time, most of these Tory gains were in North Wales in below quota-sized constituencies. But the majority of the 22 Welsh seats that Labour held on to are equally small. So, on balance, Labour should expect to lose more seats than the Conservatives in Wales.”

In Scotland, the loss of two constituencies is likely to hit the SNP. Of the seven SNP-held seats in inner Glasgow, the electorate ranges from 57,000 (Glasgow North) to over 70,000 (Glasgow South) and, calculates Lord Hayward, “Glasgow and its environs will lose at least one seat”. By contrast, “most of the Scottish Conservative-held seats are roughly the right size” so Hayward is more sanguine about the consequence of boundary changes in rural areas where the Tories are still the incumbents. Banff & Buchan (66,000 electorate; Conservative 4,000 majority over the SNP) is nevertheless among those facing redrawn boundaries.

Although there are four different Boundary Commissions, one for each of the four nations, they are working to a near identical methodology which treats all of the UK on an equal basis. They all expect to conclude their reviews by the early summer. Thereafter the consultation period with the public (and political parties) will follow, with a final report, including whatever changes the consultation period may persuade the Commission to make, being sent to the Speaker of the Commons by July 2023.

The final report will be enacted – without the right of political amendment – through what is inelegantly called “automaticity,” the 2020 Parliamentary Constituencies Act having removed the right of MPs to first vote on the changes. Thus, when the Boundary Commission’s final report is concluded that is the end of the matter – no political pressure can be applied to derail or divert the constituency map it creates. Voters throughout the United Kingdom will be more equally represented than at any time in the history of British democracy. Whether they will feel greater affinity to the constituency in which they find themselves – let alone the MP it elects – is another matter.