The four boundary commissions for England, Scotland, Wales and Northern Ireland are announcing their initial proposals for changes to Commons constituencies this autumn.
The plans for England and Wales are being published on Tuesday, following the publication of those for Northern Ireland last week. The Scottish proposals are due to be published on October 20.
:: Why all the fuss?
The plans involve massive changes to parliamentary seats, reducing the number of MPs from 650 to 600 and transforming the political landscape in advance of the general election due in 2020.
The new constituency boundaries will be the subject of fierce controversy, particularly where the main parties risk losing seats. Some argue that overall the changes generally will benefit the Conservatives and disadvantage Labour.
:: Why are the number of MPs being cut?
Tory former Prime Minister David Cameron pressed the case for reducing the number of MPs from 650 to 600 on the grounds that, firstly, there were too many when compared with the proportion of elected representatives in other parliaments around the world and, secondly, that it would save taxpayers’ money. It was seen as a measure that would prove popular after the MPs’ expenses scandal.
:: Where will the axe fall?
The number of MPs will be cut from 533 to 501 in England, from 59 to 53 in Scotland, from 40 to 29 in Wales, and from 18 to 17 in Northern Ireland. The already-published Northern Ireland plans show that Belfast is due to go from having four seats to three.
The cuts in England by region are: from 58 to 57 in the Eastern region; 46 to 44 in the East Midlands; 73 to 68 London; 29 to 25 North East; 75 to 68 North West; 84 to 83 (overall) South East; 55 to 53 South West; 59 to 53 West Midlands; 54 to 50 Yorkshire and the Humber.
:: What about the number of voters in each constituency?
Large variations in the size of constituency electorates give rise to complaints that a vote in one constituency with a large electorate has less weight than one in another constituency with a smaller electorate. Periodic boundary reviews aim to minimise discrepancies.
In the current exercise, the target size for constituencies has been set at 74,769 voters, based on the December 2015 electorate figures. But the rules for the review allow a variation of 5% above or below this “quota”, meaning constituencies should be no smaller than 71,031 and no larger than 78,507.
Exceptions to this are the Isle of Wight, which is being split into two new constituencies, and other island seats Orkney & Shetland and Na h-Eileanan an Iar (Western Isles).
:: Are there any problems with these rules?
The use of the December 2015 electorate figures has been criticised because they do not cover the significant increase in voter registration seen in the run-up to the EU referendum in June. However, the boundary commissions have no discretion to use other electorate data under the law governing the review.
The allowance for a variation of 5% above or below the quota is narrower than the 10% for which some have argued. It will mean even more difficult decisions have to be made where constituencies with historical ties to particular communities or areas are forced to undergo change.
:: Have we not been here before?
There are similarities with the previous review of constituency boundaries which was abandoned after being blocked in Parliament by the Liberal Democrats in 2013 following a row with their Conservative coalition government partners.
:: What are the main political repercussions?
It seems clear that Labour will be hardest hit. Most of the regions where Labour led at the 2010 general election will see bigger reductions, while most of those where the Conservatives were ahead will see smaller ones. This lends support to claims that most of the 43 seats that will go from England and Wales are Labour-held.
Current Labour divisions over the party leadership are likely to spill over into the selection battles for the party’s prospective candidates in new or significantly changed seats.
The SNP is bound to be affected by the reduction in Scottish representation at Westminster by six seats.
A political realignment is likely in Northern Ireland. Analysis of the initial proposals shows the various parties will face tougher competition in many seats, particularly in the three Belfast constituencies.
:: How much are the initial proposals likely to change before they are implemented?
They are likely to change significantly during the process of consultation and revision. According to the England Boundary Commission, their initial proposals under the previous review changed by 61% by the time they produced their revised proposals, before that review was abandoned.
:: Will I get a say?
You will be able to make your views known to the boundary commissions for England, Scotland, Wales and Northern Ireland at public hearings and through written representations over specified periods following the publication of their proposals.