Result · Thursday, 18 June 2026
Aberdeen South by-election
Conservative gain from SNP. Douglas Lumsden (Conservative) won on 49.5%, a 6,050-vote majority (+20.9pp) over Richard Thomson (Scottish National Party, 28.6%). Turnout 37.4%. Scotland · S14000061.
Declared result (vote share)
- Conservative 49.5% Douglas Lumsden
- Scottish National Party 28.6% Richard Thomson
- Reform UK 8.6% Jo Hart
- Labour 5.4% Nurul Hoque Ali
- Lib Dem 4.4% Mel Sullivan
- Green Party 3.4% Jorg Shelton-Eckstein
- Other 0.2%
Trigger
Why this seat was contested
Stephen Flynn (Scottish National Party) Flynn was elected to the Scottish Parliament on 7 May 2026; the Scottish Elections (Representation and Reform) Act 2025 bars a dual Holyrood+Westminster mandate, so he resigned the Commons seat on 14 May 2026.
Declared result · 18 June 2026
Full result
| Party | Votes | Share | Swing vs GE2024 |
|---|---|---|---|
| Conservative | 14,308 | 49.5% | +25.1pp |
| Scottish National Party | 8,258 | 28.6% | -4.2pp |
| Reform UK | 2,478 | 8.6% | +1.7pp |
| Labour | 1,550 | 5.4% | -19.3pp |
| Lib Dem | 1,270 | 4.4% | -1.9pp |
| Green Party | 974 | 3.4% | -0.1pp |
| Other | 59 | 0.2% | -1.2pp |
| Majority | 6,050 | 20.9pp | n/a |
| Turnout | 28,897 | 37.4% | n/a |
Source: returning officer declaration via primary record.
The signal · no constituency polls existed
What the freshest data pointed to
No published constituency polling for this by-election (confirmed by PollCheck and Ballot Box Scotland). By-elections get no broadcaster exit poll either. The signal below is the substitute.
Pre-election call: Ballot Box Scotland: Lean SNP.
7 May 2026 Holyrood overlap
Aberdeen Deeside and North Kincardine (Holyrood constituency). Stephen Flynn won this Holyrood seat on 7 May 2026, the win that triggered the Westminster by-election. Different electorate to the Westminster seat; constituency (first) vote.
- Scottish National Party 34.1%
- Conservative 30.5%
- Reform UK 17.7%
- Lib Dem 8.3%
- Labour 8.1%
GE2024 baseline (4 Jul 2024)
The year-old general-election result, a naive prior.
- Scottish National Party 32.8%
- Labour 24.7%
- Conservative 24.4%
- Reform UK 6.9%
- Lib Dem 6.3%
- Green Party 3.5%
- Other 1.4%
Scorecard · how every forecaster did
Forecasts vs result
| Forecaster | Type | Predicted winner | Share MAE | Call |
|---|---|---|---|---|
| Actual result | declared | Conservative | n/a | n/a |
| UK Elections Holyrood signal · 7 May (basis) | signal | Scottish National Party | 8.1pp | ✗ |
| GE2024 result (naive prior) · 4 Jul 2024 | baseline | Scottish National Party | 8.7pp | ✗ |
| Electoral Calculus (GE seat model) · 9 May | seat model | Scottish National Party | 9.0pp | ✗ |
| UK Elections GE seat model · 19 May | seat model | Scottish National Party | 9.6pp | ✗ |
| Betting markets (eve of poll) · 17 Jun | market | Scottish National Party (79%) | n/a | ✗ |
| Ballot Box Scotland (qualitative) · 4 Jun | qualitative | Scottish National Party | n/a | ✗ |
How every forecaster did, graded against the declared result. No constituency poll or bespoke by-election model existed for this seat; the entries are the freshest signal, the Electoral Calculus GE-model seat estimate, betting markets, and the Ballot Box Scotland qualitative call. MAE is over each forecaster's reported parties.
An upset. Every area signal pointed to an SNP hold: the GE2024 baseline (SNP 32.8%), the 7 May 2026 Holyrood overlap (SNP 34.1% ahead of the Conservatives' 30.5%), and Ballot Box Scotland's 'Lean SNP' call. The result was a 21-point Conservative GAIN, the first Conservative gain of a Westminster seat at a Scottish by-election since 1967.
The mechanism was tactical unionist consolidation on a low (37%) by-election turnout. Labour collapsed from 24.7% to 5.4% (-19pp) and the Lib Dems eased, with that vote coalescing behind Douglas Lumsden to beat the SNP. The SNP's own share barely moved (-4pp); they were not so much defeated as outflanked by a unified anti-SNP vote.
Reform UK is the signal's other big miss: 17.7% in the Holyrood overlap five weeks earlier, just 8.6% here. Reform's Holyrood list strength did not transfer to a Westminster by-election framed as a straight SNP-vs-Conservative fight. No area-level signal could have called this; it needed a model of tactical switching that the raw shares do not contain.