Boundary shakeup makes already tricky general election even more complicated

Tories would have won even larger majority in 2019 under Britain's new constituency boundaries, ITV News' Political Correspondent Romilly Weeks

Words by Colin Rallings, ITV News Election Analyst

Many electors will find themselves voting in unfamiliar constituencies at the general election later this year.

For the first time since 2010, a wholesale review of parliamentary boundaries throughout the United Kingdom undertaken by the independent Boundary Commissions has been enacted.

The review is designed to take account of the movement of population across the country and to equalise electorates.

Although the House of Commons will continue to elect 650 MPs, the number returned from England will increase by 10 with eight fewer in Wales and two fewer in Scotland.

The additional constituencies in England are concentrated in the south; the reduction in Wales from 40 to 32 seats reflects a decision to no longer allow effective over-representation there following the granting of additional powers to the Welsh Parliament/Senedd Cymru.

And it is not only electors who will notice the difference. Several MPs will find the name and character of their seats changing: even, in some cases, disappearing altogether.

The by-election due to be held in the Kingswood constituency near Bristol on February 15 provides a good illustration.

The current MP, Conservative Chris Skidmore, had already announced he would not stand at the next general election before he took the decision to resign early on a matter of policy.

Under the boundary changes, the electors of Kingswood are being dispersed to four newly drawn constituencies – nearly half of them to Somerset North East & Hanham where Jacob Rees-Mogg is the incumbent; a further third to the new Bristol North East.

Taken together these changes will also have an impact on the arithmetic of the next election – both the party political character of individual seats and the pattern of results nationwide from December 2019, which the parties will need to defend.

However, to make such calculations we need to employ surrogate information.

General election results are only counted and made available as whole constituency units and it is impossible to know precisely how particular local wards, which form the basic building blocks for the construction of constituency boundaries and which are moved about in the redistribution process, behaved.

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On the other hand, gauging the likely distribution of party support at ward level through the use of local council election results enables us to construct estimates of the notional "results" in the new constituencies as if they had existed at the time of the 2019 general election.

Doing this suggests that the boundary changes have resulted in a modest benefit for the Conservatives and a small loss for Labour.

Broadly speaking, this reflects a pattern where the East, South East and South West of England have gained seats following the increase in elector numbers, and Wales has lost them following the implementation of the new rules.

The overall impact is that the Conservatives will be defending a notional majority over all other parties of 94 at the next general election, compared with the 80 majority they achieved in 2019.

The Conservatives have made a net gain of seven seats from the new boundaries; Labour has a net loss of two seats.

The Liberal Democrats lose three seats and Plaid Cymru drops from four seats to just two.

The modest gain in seats accruing to the Conservatives from the boundary changes is reflected in a similarly modest increase in the swing from Conservative to Labour required to bring about decisive changes in the composition of the House of Commons.

Following the last general election, a direct swing of 7% from Conservative to Labour was required for Labour to become the largest party in a hung parliament.

The boundary revisions up this target for Labour to a swing of 8.3% – equivalent to an opinion poll lead of about five points over the Conservatives.

To gain an overall majority Labour needs a swing of 12.7 points and a poll lead of about 14 points, up from 12 on the old boundaries.

A more difficult task certainly, but perhaps more a matter of degree than of substance.

The swing needed is still substantially more than the 10.2% Tony Blair achieved in 1997, and indeed more than double that at any other election since 1945.

Any uniform swing from Conservative to Labour of greater than 4.2 and less than 12.7 points at the next general election is likely to produce a hung parliament with no one party having an overall majority.

A concentration on the direct swing between Labour and the Conservatives makes the implicit assumption that there will be no change in the share of votes cast for the Liberal Democrats and the Nationalist parties.

In practice, this is unlikely to be true, especially in the case of the Scottish National Party (SNP).

For example, a 10 percentage point swing from the SNP to Labour in Scotland would yield that party 15 gains under the new boundaries and ease its path towards Downing Street.

There is one further important caveat.

If they had found themselves in a new constituency with a potentially different pattern of party competition (and of campaigning by the parties) in 2019, some electors may have either voted differently or decided to cast a ballot where previously they had abstained thinking the outcome to be a foregone conclusion.

Our estimates can do no more than present an indication of the partisan impact of electors moving between constituencies based on how they voted in their old constituency at the 2019 general election.

They make no assumptions about their behaviour this year.

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