Pollster Profile
Opinium Research: Observer Poll & UK Voting Intention
Opinium Research is a full-service market research firm best known in political circles as the official polling partner of The Observer — the Sunday newspaper published alongside The Guardian. The partnership, running for over a decade, gives Opinium one of the most prominent platforms in UK political polling: Observer-Opinium polls are published on Saturday evenings each week, typically setting the political agenda for the coming week.
Opinium was founded in 2008 and has grown to become one of the UK larger independent research agencies. Unlike some rivals that are subsidiaries of large global research corporations, Opinium remains independently owned — a factor that some political clients consider an advantage when commissioning sensitive research.
Opinium methodology
Opinium conducts all its voting intention polling online, using its proprietary panel. The standard voting intention survey achieves exactly 2,000 completed interviews — a deliberate choice maintained consistently, giving a standard statistical margin of error of approximately plus or minus 2.2 percentage points at the 95% confidence level.
- Panel management: Opinium recruits panel members through online advertising, social media, and partner recruitment networks. Panel members are paid per completed survey, which Opinium argues provides better engagement than points-based systems.
- Sample design: Interlocking age-gender-region quotas ensure the raw sample broadly reflects the British adult population before weighting. Social grade quotas are also applied at the sampling stage.
- Fieldwork timing: Observer-Opinium polls run Wednesday to Friday, enabling publication in the Saturday paper. This three-day fieldwork window produces consistent turnaround.
- Weighting: Weights are applied for age, gender, region, social grade, and 2024 General Election vote recall. Opinium uses a conservative vote recall weight, applying a small correction for the known tendency of voters to claim they voted for the winning party.
- Voting intention question: Standard BPC-approved wording. Respondents who say they are undecided are offered a follow-up squeeze question asking which party they would be most likely to support. Squeezed leaners are counted as a half-weight contribution to the headline figures.
Opinium May 2026 voting intention
Opinium for The Observer, fieldwork 7–9 May 2026. n=2,000.
Recent Opinium polls: 2025–2026
| Date | Lab | Con | Reform | LD | Grn | n |
|---|---|---|---|---|---|---|
| 9 May 2026 | 27% | 22% | 26% | 13% | 7% | 2,000 |
| 2 May 2026 | 27% | 22% | 26% | 14% | 6% | 2,000 |
| 25 Apr 2026 | 28% | 22% | 25% | 14% | 6% | 2,000 |
| 18 Apr 2026 | 28% | 23% | 25% | 13% | 7% | 2,000 |
| 11 Apr 2026 | 28% | 23% | 24% | 13% | 6% | 2,000 |
| 28 Mar 2026 | 29% | 24% | 23% | 13% | 6% | 2,000 |
The Observer partnership
The Observer-Opinium partnership is one of the most consistent media-pollster relationships in UK journalism. The Observer has published Opinium voting intention data on an approximately weekly basis since 2013, giving the dataset a continuous run of over twelve years. This long consistent series allows genuine like-for-like comparisons of party support across time without methodological changes distorting the trend. The Observer typically publishes Opinium headline figures in its Saturday edition. Full data tables are published on the Observer and Opinium websites and deposited with the BPC archive.
Opinium accuracy at GE2024
At the 2024 General Election, Opinium was one of the better-performing pollsters. Its final poll showed Labour at 36%, Conservatives at 22%, Reform UK at 13%, and the Liberal Democrats at 13%. Against the actual result (Lab 33.7%, Con 23.7%, Reform 14.3%, LD 12.2%), Opinium mean absolute error was 2.8 points — second only to YouGov in the industry ranking. The firm overstated Labour by 2.3 points, understated Reform by 1.3 points, and was essentially spot-on for the Liberal Democrats. See the full accuracy table for all pollsters and elections.
Opinium house effects
Opinium sits close to YouGov in the polling distribution. The two firms typically produce similar Labour and Conservative figures. Reform UK is marginally lower with Opinium than YouGov on average (roughly 1 point). The Lib Dem figures are nearly identical between the two firms. Opinium Green Party figures are slightly higher than the cross-firm average, possibly reflecting the slightly younger skew of the Observer readership. For the full house-effect analysis including Opinium adjustment factors, see the house effects explainer.