LDER’s Denis Mollison Warns AMS Faces Overhang Crisis

Denis Mollison, former Chair of Liberal Democrats for Electoral Reform (LDER), has sounded the alarm over flaws in the proportional voting system used in Scotland's Holyrood elections.

Writing in Lib Dem Voice, Denis argues that the system, called the Additional Member System (AMS) or Mixed Member Proportional (MMP), long used in Scotland, Wales and the London Assembly, is increasingly undermined by “overhangs” as more parties gain significant vote shares.

Recent Scottish polling suggests that in next year's Holyrood elections, the SNP could win 62 of 129 seats — 48% of the chamber — despite a proportional entitlement of just 33%. Denis highlights that this distortion, caused when a party secures more constituency seats than its list vote justifies, could hand the SNP 19 overhang seats next May, reducing representation for Labour, Reform, Conservatives, Liberal Democrats and Greens.

Germany, which pioneered AMS, has faced similar challenges. It initially added hundreds of seats to preserve proportionality, but in 2025 disallowed 23 constituency winners to cap parliament at 630 seats. Denis warns that with five parties in contention in England and six in Scotland, AMS risks delivering majority governments on minority votes. He insists that advocates of this particular system of proportional representation must confront this flaw if AMS is to remain credible.

His analysis is clearly not a general dismissal of proportional representation for a fairer voting system. As Denis writes, “Proportional Representation is clearly the answer to the democratically unacceptable disproportional results of First-Past-the-Post FPTP (FPTP) elections”. At LDER, we have long advocated the Single Transferable Vote system: you can read about how it works and why it is the best system for elections in the UK here.