Rev. 20 Jan 26
FPTP. UK currently has 650 single-seat constituencies: England 543, Wales 32, Scotland 57, Northern Ireland 18. Each elects one MP by means of a First Past The Post ballot.
PV entails no boundary changes. A simple Optional Ranked Chioce ballot would elect MPs in the same single-seat constituencies. It could beneficially be implemented without delay. And it would provide a good foundation for any preferred form of PR.
Full STV requires multi-seat constituencies. This need entail no boundary changes other than the grouping of existing constituencies. In its most doctrinaire form, STV requires all constituencies to have 5 seats. But that is not a readily acceptable option.
(a) Having 103 constituencies of 5 seats requires some to cross national borders’
(b) Some existing constituencies are already impactically large (One covers 4,930 sq mi).
So assume that although most constituencies could have 5 seats some might have only 2 or 3.
Progressive STV, on the other hand, would work from the other end. Starting with the implementation of pure PV (STV in single-seat constituencies), it would group constituencies progressively, with due consideration to
(a) practicality (i.e. not making constituencies unmanageably large)
(b) coherence (in particular, not partnering disparate area just to make up numbers)
(c) consistency (taking note of national and county boundaries).
All of which could result in the retention of many 1-seat constituencies, and the establishment of many with 2 or 3 seats. Which result could be even more likely if the local voters are consulted on all envisaged groupings.
AMS (the “Additional Member System”) is a hybrid which seeks to increase the party-proportionality which FPTP, PV and STV so obviously lack while retaining the directly representative democracy on which FPTP and PV are explicitly based. It does so by retaining single-seat constituencies and in addition having a “top-up” proportion of MPs elected by a regional party-list vote to get as close as possible to overall proportionality.
An appropriate top-up proportion remains to be decided (44% in London, 43% in Scotland, 15%-20% proposed by Jenkins). But in all cases, unless we have a significant increase in the number of MPs, which is not generally proposed, we would be forced to undertake a significant adjustment of our single-seat constituencies. Which is bound to take a long time.
Full PR, on the other hand, would require no boundary changes, other than perhaps grouping existing constituencies into coherent voting regions.