Parliamentary boundary changes are an unavoidable necessity for our electoral system, or at least, they are necessary if you want to avoid rotten boroughs and wildly differing electorates from seat to seat. Exactly how they are carried out, however, is an intensely political decision. The frequency of reviews and the rules that the Independent Boundary Commissions must follow make significant differences to election results.

As a general rule the population in the Home Counties and London commuter belt rises faster than the population in Northern towns and, as such, the electorate of Tory seats tends to grow faster than Labour seats. Hence whenever Parliamentary boundaries are updated, Tory voting areas have gained extra seats and Labour voting areas have lost seats. It has always been in the Conservatives’ electoral interests to hurry along boundary reviews as much as possible, and in Labour’s interest to delay them. Equally, because the Boundary Commissions tend to avoid change unless necessary, the more strictly the rules on electorate size are applied, the more the reviews help the Conservatives.

Over the years these apparently dull administrative changes have therefore been political battlegrounds. In 1969 the Labour government successfully voted to block the implementation of the boundary review so they could fight the 1970 election on old boundaries.  Ahead of the 1983 election Michael Foot tried and failed to get the courts to block the implementation of the next review. In 1992 John Major changed the law to bring forward the review and get new boundaries in time for the 1997 election, not that it did him much good.

When David Cameron came to power in 2010 he again sought to speed up the process in the Tories’ favour. From now on, there would be a review every five years, the rules would be changed to prioritise equality of electorate over other considerations, with all seats (bar a handful of geographical exceptions) within 5% of a uniform quota. The number of MPs would also be cut from 650 to 600. The reduction in seats was viewed with suspicion by opposing parties who assumed the arbitrary number had been picked to favour the Conservatives. I suspect the truth was more straightforward, there was nothing particularly special about the number, but the reduction allowed Cameron to claim that the reduction was about cutting the cost of politics, rather than just bringing a boundary review forward for political benefit.

Labour saw the changes as a naked attempt to move the boundaries in the Conservatives’ favour and without cross-party support the 2011 review fell apart as coalition relations soured. While the review would have helped the Conservatives, it did nothing for the Liberal Democrats. Originally it had been the quid-pro-quo for the Liberal Democrats desired referendum on AV, but after the Conservatives abandoned reform of the House of Lords the Liberal Democrats pulled their support.

Neither did the 2015 review manage to progress. While David Cameron had scraped a majority, it was always going to be difficult to pass a boundary change that involved 50 members of Parliament losing their jobs. Most of those may have been Labour MPs, but that was scant consolation for the Tory MPs losing their constituencies. Equally, the stricter rules produced more awkward seats and local campaigns opposing them. A seat crossing between Cornwall and Devon was mathematically impossible to avoid but seen as an outrageous heresy by some Cornish MPs.

With a solid majority Johnson has the numbers to finally force through a boundary review on Cameron’s rules

If the Cameron government had just left the rules alone then a review would likely have gone ahead in time for 2019 on the old rules and the old timetable. As it was, the May government failed to bring the completed boundaries in front of the House, claiming it was taking a long time to draft the legislation, but more likely avoiding inevitable defeat in the face of the solid opposition from other parties.

With a solid majority to play with Boris Johnson has the numbers to finally force through a boundary review on David Cameron’s rules. The government announced last week that they would not. Instead they will amend the rules, going back to a House of Commons of 650 MPs and reviews every eight years or so.

This looks like an attempt at compromise, but it is compromise on Conservative terms. The Boundary Commissions will still undertake the review on rules requiring them to prioritise equal electorates over other considerations, and will still require the electorate of almost all seats to be within a tight 5% band around the national quota. The rules will still be stricter than those used for the previous reviews.

Perhaps a more advantageous change is that the Government propose changing the law so that Parliament will no longer be required to vote in favour of the new boundaries for them to take effect. Instead they would be implemented through Orders in Council, reducing the chance of future reviews from being blocked and meaning the Conservatives can once again look forward to regular boundary reviews.

However, as the Tories finally look set to get the boundary changes they want, it’s worth noting that it is not inevitable that they will always favour the Conservatives.

Once upon a time, when seats were lost in declining post-industrial Northern towns it would only ever damage the Labour party. Following the 2019 election the Conservatives suddenly have their own Members of Parliament in just those declining areas. Equally some of the areas with the fastest growing populations are multicultural areas of London, or inner-city Manchester – areas that remain solidly Labour. The forthcoming boundary review will likely still help the Conservatives, but perhaps they will not always be quite such a one-way bet for the party.